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					                              The CREDOS Project

              Final Concept of operations description



                                               Abstract:
 This document describes version E of the final generic Concept of Operations for Crosswind-
 Reduced Separation for Departure Operations (CREDOS).

 The CREDOS project is investigating the possibilities of safe conditional reduction of separation
 minima for departure, by suspending the wake turbulence separation minima under specific
 crosswind conditions, resulting in improved runway throughput.




Contract Number:         AST5-CT-2006-030837         Proposal Number:            30837
Project Acronym:         CREDOS
Project Co-ordinator:    EUROCONTROL
Document Title:          Final Concept of operations description            Deliverable Nr:     D4-11
Delivery Date:           November 2009
Responsible:             ECTL – M3S
Nature of Deliverable:   Report                      Dissemination level:        Public
File Id N°:              CREDOS_410_ECTL_DLV_4-11_CONOPS.doc
Status:                  Approved                    Version:      1.0   Date:            20/11/2009


                                           Approval Status
       Document Manager                 Verification Authority                   Project Approval
               ECTL                               NLR                                     PMC
          Anna Wennerberg                 Lennaert Speijker                        PMC members
                                             WP4 Leader
                                FINAL CONCEPT OF OPERATIONS DESCRIPTION



                                           Executive Summary
        This document describes the final Concept of Operation for Crosswind departures, called
        CREDOS. The CREDOS Concept of operation will be developed in the context of the CREDOS
        project.

        Increases in air traffic over recent years have resulted in congestion at many major airports. The
        need to increase airport capacity, while maintaining levels of safety, is one of the major
        challenges facing ATM research today.

        Extending existing airport infrastructure is expensive, requires a long lead time and is often not
        an option due to environmental considerations. Methods of improving runway throughput using
        only the existing infrastructure are of increasing interest.

        The application of ICAO wake turbulence separation minima is effective in avoiding potentially
        dangerous wake turbulence encounters but it also reduces runway throughput due to the
        additional distance to be maintained between certain aircraft pairs. In addition, these separation
        minima have been set out to be applied regardless of the meteorological conditions, and hence
        are over-conservative in certain weather conditions, and therefore unnecessarily reduce airport
        capacity.

        Among other potential solutions, the CREDOS project is investigating the possibilities of safe
        conditional reduction of separation minima for departure, by suspending the wake turbulence
        separation minima under specific crosswind conditions, resulting in improved runway
        throughput.

        The basic idea behind CREDOS is that, for departure, the wake turbulence separation criteria
        may be relaxed on the runway and for the first part of the climb path when the crosswind is such
        that the wake turbulence generated by the preceding aircraft should have been blown out of the
        departure track of the succeeding aircraft.

        The CREDOS benefits arise from a temporary increase in runway throughput. This increase
        occurs only when a lighter aircraft directly follows a heavier one and the crosswind requirements
        are met. Only in this case is there a potential for reducing the spacing between that aircraft pair
        compared to the wake turbulence separation that would otherwise have to be applied.

        Emphasis is to be put on the fact that CREDOS is not expected to add strategic capacity in
        terms of scheduled slots.

        The major benefits are to be achieved when a single segregated runway is used for departing
        traffic and during peak periods or when queuing creates delays of departing traffic at the
        runway. An actual change in the declared runway capacity may be published only if a longer
        period of stable crosswind conditions is forecast.

        The actual benefits are dependent on local wind conditions, traffic composition, the usage of the
        runway and the SID structure. So far only the case of a single independent runway used for
        departures only has been explored, but there is reason to believe that there would also be
        benefits in more complex situations.



EUROCONTROL                                                                                                                    Page 2

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                                   FINAL CONCEPT OF OPERATIONS DESCRIPTION



Table of Contents
1. INTRODUCTION.....................................................................................................................................7 

     1.1. Background ............................................................................................................................................ 7 

     1.2. Purpose of the Document..................................................................................................................... 7 

     1.3. Structure of the Document ................................................................................................................... 8 

     1.4. Terminology and definitions ................................................................................................................ 8 


2. THE NEED FOR CHANGE............................................................................................................... 10 

     2.1. Context – Need for more Airport Capacity....................................................................................... 10 

     2.2. ICAO Separation minima .................................................................................................................... 11 

     2.3. Solution Proposed by credos ............................................................................................................ 12 

     2.4. Meeting the SESAR Objectives.......................................................................................................... 12 


3. CREDOS CONCEPT OF OPERATIONS..................................................................................... 13 

     3.1. Scope and Assumptions .................................................................................................................... 13 

     3.2. Concept Description – Crosswind Departures................................................................................ 16 
          3.2.1. Minimum reduced spacing................................................................................................................... 17  
          3.2.2. Determination of the size of the WTSSAV ........................................................................................ 18  
          3.2.3. Determination of the CREDOS spacing ............................................................................................ 19  
          3.2.4. SID considerations................................................................................................................................ 20 
          3.2.5. CREDOS departure process (example) ............................................................................................ 21  
          3.2.6. Application of CREDOS spacing ........................................................................................................ 22  

     3.3. CREDOS Operation in the current ATC/ATM Environment ........................................................... 23 
          3.3.1. Definition of CREDOS roles and procedures ................................................................................... 23 
          3.3.2. Wind strength and direction................................................................................................................. 32  
          3.3.3. CREDOS system status....................................................................................................................... 33  
          3.3.4. CREDOS HMI and support tools ........................................................................................................ 35  
          3.3.5. What is needed before local implantation? ....................................................................................... 38  
          3.3.6. CREDOS System requirement ........................................................................................................... 39  
          3.3.7. CREDOS User Requirement............................................................................................................... 39  
          3.3.8. CREDOS Operational Requirement .................................................................................................. 39  


4. EXPECTED BENEFITS OF THE CREDOS CONCEPT.......................................................... 40 


EUROCONTROL                                                                                                                                       Page 3

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                                    FINAL CONCEPT OF OPERATIONS DESCRIPTION


5. CONCLUSIONS AND FUTURE OPTIONS................................................................................. 42 

6. CONCEPT EVOLUTION ................................................................................................................... 44 

     6.1. Timeline................................................................................................................................................. 44 

     6.2. Changes in version B compared to A............................................................................................... 44 

     6.3. Changes in version C compared to B............................................................................................... 45 

     6.4. Changes in version D compared to C............................................................................................... 46 

     6.5. Changes in version E compared to D ............................................................................................... 46 


7. REFERENCES ..................................................................................................................................... 47 

8. LIST OF FIGURES.............................................................................................................................. 49 

9. LIST OF TABLES................................................................................................................................ 51 




ANNEXES ................................................................................................................................................... 52 

A. EXAMPLE OF CREDOS IMPLEMENTATION (USED FOR CREDOS REAL-TIME
SIMULATIONS)......................................................................................................................................... 53 

B. USE CASES ......................................................................................................................................... 65 

C. CREDOS TOWER CONTROL SURVEY REPORT 2008 ...................................................... 76 




EUROCONTROL                                                                                                                                       Page 4

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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION




        ACRONYMS USED IN THE REPORT
                       ACC        Area Control Centre
                        AIP       Aeronautical Information Publication
               A-SMGCS            Advanced Surface Movement Guidance and Control System
                      ATIS        Automatic Terminal Information Service
                       ATM        Air Traffic Management
                                  Essential information for flight crews about a specific airport broadcasted on a
                                  designated frequency. Data provided is local weather conditions, runway in
                                  use, constraints and other useful information.
                       ATC        Air Traffic Control
                     ATCO         Air Traffic controller
                       ATS        Air Traffic Service
                     CFMU         Central Flow Management Unit
                CREDOS            Crosswind-Reduced Separation for Departure Operations
                     CTOT         Calculated Take-off Time (CFMU)
                    DMAN          Departure Manager
                                  An ATM system tool that assists controllers with sequencing, metering and
                                  advisory service for the traffic flow management of departing traffic.
                       FAA        Federal Aviation Administration
                        HMI       Human Machine Interface
                      ICAO        International Civil Aviation Organisation
                        IFR       Instrumental Flight Rules
                    LIDAR         Laser Imaging Detection And Ranging
                                  Technology used to measure atmospheric parameters (wind speed and
                                  direction, humidity, aerosol, …) and also wake vortices.
                     NASA         National Aeronautics and Space Administration, USA
                     NATS         National Air Traffic Services, United Kingdom
                       NLR        Nationaal Lucht- en Ruimtevaartlaboratorium – Dutch National Aerospace
                                  Laboratory
                         NM       Nautical Miles
                                  Navigation measure equal to 1852 m.
                        SID       Standard Instrument Departure (Route)
                                  SID standard ATS routes identified in an instrument departure procedure by
                                  which aircraft should proceed from take-off phase to the en-route phase.
                       TMA        Terminal Manoeuvring Area
                                  A control area normally established at the confluence of ATS routes in the
                                  vicinity of one or more major aerodromes.
                       VFR        Visual Flight Rules
                                  Set of regulations which allow a pilot to operate an aircraft using visual
                                  navigation, when weather conditions permit. Specifically, the weather must
                                  meet the Basic VFR Weather Minimums (defined by the relevant aviation
                                  authority).


EUROCONTROL                                                                                                                    Page 5

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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION


        ACRONYMS USED IN THE REPORT
                WTSSAV            Wake Turbulence Separations Suspension Airspace Volume (acronym
                                  developed for CREDOS)
                                  Volume surrounding the aircraft departure path within which the wind can be
                                  monitored and within which the wake turbulence separation may be suspended
                                  (see section 3.2.2).
                        WV        Wake Vortex
                                  Also known preferably by ICAO as wake turbulence. Wake turbulence is
                                  turbulence that forms behind an aircraft as it passes through the air. This
                                  turbulence includes various components, the most important of which are
                                  wingtip vortices and jetwash. Jetwash refers simply to the rapidly moving air
                                  expelled from a jet engine; it is extremely turbulent, but of short duration.
                                  Wingtip vortices, on the other hand, are much more stable and can remain in
                                  the air longer after the passage of an aircraft. Wingtip vortices make up the
                                  primary and most dangerous component of wake turbulence. Wake turbulence
                                  is especially hazardous during the landing and take-off phases of flights, for
                                  two reasons. The first is that during take-off and landing, aircraft operate at low
                                  speeds and high angle of attack. This flight attitude maximizes the formation of
                                  dangerous wingtip vortices. Secondly, take-off and landing are the times when
                                  a plane is operating closest to its stall speed and to the ground - meaning there
                                  is little margin for recovery in the event of encountering wake turbulence.




EUROCONTROL                                                                                                                    Page 6

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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION



1. INTRODUCTION
        The Crosswind-Reduced Separation for Departure Operations (CREDOS) is a project of the
        Sixth Framework Programme of the European Commission (DG-RTD) co-ordinated by
        EUROCONTROL.

        The CREDOS project involves eleven European organisations (Airbus, Berlin Technical
        University, DFS, DLR, EUROCONTROL, INECO, M3 Systems, NATS, NLR, ONERA and the
        Université catholique de Louvain) and has been carried out in close collaboration with the FAA.
        The project started in June 2006 and ends in November 2009.


1.1. BACKGROUND
        Increases in air traffic over recent years have resulted in congestion at many major airports. The
        need to increase airport capacity, while maintaining levels of safety, is one of the major
        challenges facing ATM research today.

        Extending existing airport infrastructure is expensive, requires a long lead time and is often not
        an option due to environmental considerations. Methods of improving runway throughput using
        only the existing infrastructure are of increasing interest.

        One potential solution for increasing runway throughput would be to replace the original, static,
        and hence often over-conservative, wake turbulence separation minima with lower minima
        based on actual meteorological conditions.

        In this context, the CREDOS project is investigating the possibility of a safe conditional
        reduction of wake turbulence separation minima under specific crosswind conditions.

        Although limited in its scope to single runway departures and certain wind conditions, the
        CREDOS concept of operations offers a possible solution for temporarily increasing runway
        throughput.


1.2. PURPOSE OF THE DOCUMENT
        The purpose of this document is to provide a generic description of the CREDOS concept of
        operations in the context of current and future European Air Traffic Management.

        Since this concept aims to be generic, the procedures described here may differ depending on
        local circumstances, including the user interface. This material is to be considered as guidance
        only and is not meant to indicate endorsement of any particular solution.




EUROCONTROL                                                                                                                    Page 7

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1.3. STRUCTURE OF THE DOCUMENT
        Section 1                 introduces the background and the purpose of the CREDOS concept of
                                  operations document.

        Section 2                 addresses current airport limitations and the potential solution brought by the
                                  CREDOS concept.

        Section 3                 describes the CREDOS concept and how it can be operated in the current
                                  ATC/ATM environment.

        Section 4                 presents the expected benefits of the CREDOS concept.

        Section 5                 concludes and presents future development options.

        Section 6                 describes the evolution of the concept throughout the project.



        As appendix:

        Annex A                   describes how CREDOS concept of operations has been implemented for
                                  the real-time simulations.

        Annex B                   presents the use cases.

        Annex C                   presents the CREDOS tower control survey report (2008).


1.4. TERMINOLOGY AND DEFINITIONS
        CREDOS active/non-active: CREDOS system status that reflects when CREDOS is in
            operation. Once CREDOS is activated by the tower supervisor, the status is displayed on
            the appropriate controller position HMI (see section 3.3.4). CREDOS operations may only
            be applied when CREDOS is ‘active’. When ‘non-active’, standard operations are applied.

                 Further details are provided in section 3.3.3.

        CREDOS available/not available: CREDOS system status that reflects system availability.
            ‘Available’ indicates that the CREDOS system is working correctly from a system point of
            view. When ‘not available’, CREDOS cannot be activated.

                 Further details are provided in section 3.3.3.

        CREDOS wind level: A set of conditions, determined by the appropriate ATS authority, all of
            which must be satisfied for CREDOS spacing (see hereafter) to be applicable on a given
            runway between a given pair of departing aircraft. Conditions include the crosswind
            component, but could also include the steadiness of wind speed and direction or
            significant weather changes such as thunderstorms or wind shear. Specific CREDOS
            levels may be defined for activating/deactivating CREDOS.

        CREDOS spacing: The minimum longitudinal position difference that must exist between two
            departing aircraft at the time the take-off clearance is issued to the second aircraft in
            cases where the wake turbulence separation minima may be suspended in accordance
            with the applicable CREDOS criteria (such as crosswind conditions or SID geometry).


EUROCONTROL                                                                                                                    Page 8

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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION


                 The position difference is referenced to the leading aircraft and may be expressed in time
                 elapsed since start of the take-off roll, or distance covered from start of the take-off roll (or
                 both). The CREDOS spacing is lower than that resulting from the use of wake turbulence
                 separation minima but never less than the current corresponding minima applicable when
                 an ATS surveillance service is provided.

        Crosswind: In this document ‘crosswind’ should be understood as the crosswind component
             perpendicular to a specific runway direction.

        Departure controller: Controller in the approach sector who controls the departures.

        Flight crew: In this document a generic term used to identify any licensed crew member charged
               with duties essential to the operation of an aircraft during a flight duty period.

        GO/NO-GO: CREDOS HMI solution that will indicate to the runway controller whether or not
            CREDOS operations can be applied for a specific following aircraft. This solution can be
            simple and solely based on crosswind data or more advanced, taking into account further
            meteorological input, flight plan data and radar data.

                 Further details are provided in section 3.3.3.

        Wake turbulence: In compliance with ICAO usage, in this document the term ‘wake turbulence’
             is used to describe the effect of the rotating air masses generated behind the wing tips of
             large jet aircraft, in preference to the term ‘wake vortex’ which describes the nature of the
             same phenomena.

        The terminology used in this document is aligned to the terminology defined/used in the SESAR
        programme as requested by the European Commission.




EUROCONTROL                                                                                                                    Page 9

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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION



2. THE NEED FOR CHANGE

2.1. CONTEXT – NEED FOR MORE AIRPORT CAPACITY
        The EUROCONTROL Performance Review Commission Report [3] published in April 2004
        recorded that the cost and impact of airport-related delays had reached parity with those for en-
        route and noted that airports were now a major constraint to growth.

        The same conclusion was reached in the EUROCONTROL “Constraints to Growth” study [5]. It
        predicted that if traffic demand continues to grow, even at a conservatively predicted rate, and
        airport throughput capacity problems are not resolved, some 30% of traffic demand will not be
        accommodated.

        In addition, it is commonly recognised that in today’s operations airport capacity is constrained
        inter alia by the application of wake turbulence separation minima.

        Consequently, years of effort have been put into the investigation of potential solutions to
        reduce the wake turbulence separation minima. Wake vortex research is being undertaken both
        in Europe and in the United States with a high level of collaboration especially through the
        thematic networks WakeNet-Europe and WakeNet-USA as well as the EUROCONTROL-FAA
        Action Plan 14 (AP14). The collaborative research performed to date has led to general
        consensus on the long-term vision and the identification of short-term changes that can be
        implemented to make early gains. The combined research efforts in Europe and the USA have
        already produced significant insights into the phenomenon.

        Long-term research activities are being aimed at the eventual production of a Wake Vortex
        Prediction & Monitoring System (as described in the ATC-Wake project in Europe and the
        WakeVAS Phase III project in the USA). Such a system would be equipped with weather
        nowcasting and forecasting facilities as well as WV detection and prediction tools, and would be
        integrated into the traffic sequence management process. However, earlier benefits can be
        anticipated from the implementation of intermediate solutions which do not require major
        technological advances. As knowledge of the wake vortex phenomenon increases, it is possible
        to consider near-term modifications of the separation standards, under precisely specified
        conditions.

        The USA ConOps Evaluation Team has produced two very comprehensive reports on the
        potential for Crosswind–dependent Arrivals [7] and Crosswind-dependent Departures [8].
        Crosswind concepts are the main element of the USA Mid-Term planning. Although other
        weather conditions involving turbulent air are also conducive to reduced wake turbulence
        separations, these are not yet being considered among the mid-term solutions. Technology for
        the forecasting and characterisation of turbulence needs to become more mature before
        operational concepts based on these other weather conditions can be anticipated.

        This is the general context in which the Crosswind Reduced Separations for Departure
        Operations (CREDOS) project is being developed.




EUROCONTROL                                                                                                                  Page 10

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                                 FINAL CONCEPT OF OPERATIONS DESCRIPTION


2.2. ICAO SEPARATION MINIMA
          In the 1970s, the International Civil Aviation Organisation (ICAO) implemented wake turbulence
          separation minima in order to ensure that the spacing between two aircraft is such that the
          follower aircraft does not enter into an unsafe situation due to the wake turbulence of a
          preceding aircraft.

          To set out the separation minima, aircraft types have been grouped into three wake turbulence
          categories according to their maximum take-off weight (see ICAO Doc. 4444 [9], paragraph
          4.9.1.1):

                    HEAVY – all aircraft types of 136,000 kg or more;

                    MEDIUM – aircraft types less than 136,000 kg but more than 7,000 kg;

                    LIGHT – aircraft types of 7,000 kg or less.

          The wake turbulence separation minima described in ICAO Doc. 4444 document (see
          paragraph 8.7.3.4 in [9]) are summarised in Table 1:

                                                                                                           Runway Separation
                   Leading Aircraft           Following Aircraft              Radar separation                 Time for
                                                                                                            Departures (min)
                       HEAVY                        HEAVY                           4.0 NM                            -
                       HEAVY                       MEDIUM                           5.0 NM                            2*
                       HEAVY                         LIGHT                          6.0 NM                            2*
                      MEDIUM                         LIGHT                          5.0 NM                            2*
            * 3 minutes if taking off from an intermediate position
                     Table 1: Current wake turbulence separation minima for departures.

          ICAO Doc. 4444 prescribes that the wake turbulence radar distance separation minima are to
          be applied in the departure phase of a flight where:

                    an aircraft follows or crosses behind a heavier aircraft,

                    both aircraft depart from the same runway or closely spaced runways,

                    or vertical separation is less than 1,000 ft.

          For departures, the runway time separations and radar distance separations shown in Table 1
          are generally applied, although reductions are allowed if aircraft depart with a visual separation
          clearance.

          In addition to the wake turbulence separation minima, ICAO Doc. 4444 recommends that the
          horizontal separation minimum based on radar and/or ADS-B shall be 5 NM (paragraphs 8.7.3.1
          and 8.7.3.2). It also states that this radar separation minimum may be reduced (if allowed by the
          appropriate ATS authority) to 3.0 NM, where surveillance system capabilities permit 1 .




1
    It is to be noted that, in case of succeeding aircraft established on the same final approach track, this radar separation minimum may

be reduced to 2.5 NM under specific conditions (see [9] for detailed information).

EUROCONTROL                                                                                                                  Page 11

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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION


2.3. SOLUTION PROPOSED BY CREDOS
        The ICAO wake turbulence separation minima have been set out to be applied regardless of the
        meteorological conditions. Of course applying such minima is effective in avoiding potentially
        dangerous wake turbulence encounters but it also reduces runway throughput due to the
        additional distance to be maintained between certain aircraft pairs. Moreover, it is recognized
        that these separation minima are over-conservative in certain weather conditions and therefore
        unnecessarily reduce the airport capacity.

        The CREDOS project is investigating the possibility of safely reducing separation minima for
        departures by suspending the wake turbulence separation minima under specific crosswind
        conditions, resulting in improved runway throughput.


2.4. MEETING THE SESAR OBJECTIVES
        The CREDOS concept development is in line with SESAR objectives. CREDOS was identified
        during the SESAR definition phase as one of the possibilities for improving airport capacity and
        reducing delays at airports.

        Specifically, the document “WP3.2.2 - Identification of limits-blocking points for Airport - SESAR
        definition phase - DLT-0607-322-00-07” identified one airport limits-blocking point - OP-8
        “Quality of surveillance and wake-vortex-prediction limiting in-trail and diagonal separation
        especially in low visibility”.




EUROCONTROL                                                                                                                  Page 12

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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION



3. CREDOS CONCEPT OF OPERATIONS
        The basic idea behind CREDOS is that, for departure, the wake turbulence separation criteria
        may be relaxed on the runway and for the first part of the climb path when the crosswind is such
        that the wake turbulence generated by the preceding aircraft should have been blown out of the
        departure track of the succeeding aircraft.

        The benefit of such a suspension of the wake turbulence separation would be a reduction of the
        aircraft take-off interval. This would enable a temporary increase of the departure runway
        throughput in such a way that it absorbs capacity peaks and/or reduces departure delays.

        The possibility of suspending the wake turbulence radar separation minima is highly dependent
        on the first part of the trajectories of the aircraft (e.g. location and height of the first turning
        point). It is also dependent on whether the second aircraft flies upwind or downwind of the
        preceding one. Therefore, such an airborne suspension has to be determined per airport, per
        runway and even per aircraft pair, taking into account the respective Standard Instrument
        Departure (SID).

        The following sections describe the CREDOS concept. At first the scope of the concept is
        defined, and the assumptions made are explained. Then the basic concept idea of suspending
        the wake turbulence separation minima when wind conditions permit are presented. There is
        also a description of how the wind monitoring, required for CREDOS application, defines an
        airspace volume within which CREDOS may be applied, and how the size of this volume
        determines the CREDOS spacing minimum. Finally, this document considers the impact of the
        aircraft SID on CREDOS application.

        After a description of the concept itself, the proposed integration of the CREDOS concept into
        the current ATC/ATM environment are described; proposed roles and procedures, wind
        monitoring requirements, proposed HMI and support tools.

        It is to be noted that an example of CREDOS implementation (used for the real-time
        simulations, CREDOS work package 4.3) is provided in Annex [A].


3.1. SCOPE AND ASSUMPTIONS
        The proposed concept aims for a reduction of the 2-minute start interval currently applied for
        HEAVY – MEDIUM, HEAVY – LIGHT or MEDIUM – LIGHT (see Table 1, in section 2.2) aircraft
        combinations through the suspension of both the runway wake turbulence time separation and
        the wake turbulence radar separation during take-off and first climb phase, when enabled by
        favourable crosswind conditions. The intention is not to introduce any new intermediate wake
        turbulence separation, but to totally suspend it, when a predefined CREDOS wind level is
        present.

        The CREDOS concept is based on today’s technical environment. It does not require advanced
        tools such as DMAN or electronic flight strips and it is focussing on how to accommodate a
        single independent runway used in a segregated mode for departures only.

        The concept gives most benefits during peak periods or when delays create queuing traffic at
        the runway. But it can be applied whenever the CREDOS crosswind requirements are met.


EUROCONTROL                                                                                                                  Page 13

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          CREDOS only brings benefits when an aircraft immediately follows a heavier aircraft and when
          no other constraints require spacing or separation equal to or larger than the wake turbulence
          separations.

          Upwind & Downwind SIDs

          It is proposed in the concept to introduce a distinction between upwind and downwind SIDs.
          Indeed, CREDOS is based on the lateral transport of the wake turbulence due to the crosswind,
          therefore, the suspension of the wake turbulence separation minima may only be applied if the
          departing route of the second aircraft does not go in the direction where the wake turbulence
          generated by the first one is blown (i.e. the SID of the second aircraft is not downwind from that
          of the leader). In other words, CREDOS may be applied only for an aircraft departing on the
          same or an upwind SID compared to the departure of a preceding heavier aircraft.

          In the context of CREDOS, the suspension of wake turbulence separation minima concerns only
          the runway and the first part of the climb phase 2 . Consequently, it should be possible to
          unambiguously identify upwind and downwind SIDs, even in the case of sharp turns shortly after
          the end of the runway. In any case, if upwind and downwind SIDs cannot be clearly determined,
          the proposed concept must not be applied for those particular SIDs.

          A GO / NO-GO methodology

          When CREDOS may be applied, the runway controller will be able to determine for every
          departure behind a heavier aircraft whether or not CREDOS criteria such as crosswind
          conditions or SID geometry are met. It is thus proposed that the runway controller applies a
          GO/NO-GO 3 methodology per aircraft pair.

          Assumptions

          The concept is based on the assumption that:

                    departures are controlled in an ATS surveillance system environment;

                    ATS surveillance system based separation minima are applied between aircraft after
                     departure;

                    the runway controller is responsible for establishing ATS surveillance system based
                     separation minima for departing aircraft;

                    a single independent runway is used in a segregated mode for departures only.

          It is also assumed that local validation will be done through the collection of measurement data
          with LIDAR and wind meters that will prove that a safe crosswind component can be determined
          for the runway and the first part of the climb path. In order to determine the sensitivity and
          accuracy criteria for the required wind (buffers included), other wind and weather data will also



2
    It has to be determined locally to which height CREDOS can be applied per runway, depending of the wind monitoring capabilities and

the SID structure.

3
    See terminology (section 1.3).

EUROCONTROL                                                                                                                  Page 14

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        be used. When CREDOS is in operation, only the crosswind component for the selected
        departure runway has to be measured and presented to ATC.

        Beyond the scope of CREDOS

        The suspension of the 3-minute wake turbulence separation rule when departing from an
        intersection (see Table 1) has not been considered in the concept. Similarly, super-HEAVY
        aircraft, such as the Airbus 380, have not been included.

        CREDOS focuses only on static spacing for departures.

        Crosswind concepts applied for mixed-mode runways, dependent runways and for arrivals have
        yet to be developed.




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3.2. CONCEPT DESCRIPTION – CROSSWIND DEPARTURES
        The CREDOS concept consists in authorising, on the runway and during the initial part of the
        climb, a suspension of the wake turbulence separation minima (distance and/or time) between
        certain pairs of departures when the crosswind component is such that the wake turbulence
        generated by a preceding aircraft should be blown out of the path of the succeeding aircraft.

        CREDOS wind level (see terminology), and first of all the minimum crosswind component
        threshold required, has to be determined by local validation on the basis of measurement data
        collection with LIDAR and wind meters.

        The first results of CREDOS work package 2 (see [12]), based on measured and modelled wind
        and vortex behaviour, indicates that concerning the wake turbulence transport only a crosswind
        component of about 7 kts for a separation of about 90 seconds is a reasonable assumption for
        the minimum crosswind threshold limit needed for safe CREDOS application. It is to be noted
        that 7 kts is far below the acceptable crosswind limit for take-off set by aircraft operators.

        The SID structure and other local parameters might mean that a higher, or somewhat lower,
        crosswind threshold is needed. It is also foreseen that certain buffers to avoid flickering of the
        GO/NO GO indication would be necessary. More investigation at (at least) one selected pilot
        airport is already foreseen as part of SESAR WP 6.8.1 in order to determine the exact value of
        the crosswind needed.

        Since it is wind dependent, the application of the concept requires that wind conditions have to
        be monitored in the aircraft departure area. The extent of the concept is thus dependent on the
        wind monitoring capabilities of the airport, since the concept obviously does not apply where the
        wind cannot be accurately evaluated. Wind monitoring is based on wind measurements but
        could also include wind nowcast and/or wind forecast.

        These wind determination capabilities define a volume surrounding the aircraft departure path
        within which the wind can be monitored and therefore within which the wake turbulence
        separation may be suspended. In the context of the CREDOS concept, this volume is named
        ‘Wake Turbulence Separations Suspension Airspace Volume’ (WTSSAV), see Figure 1. The
        determination of the WTSSAV size is described in section 3.2.2.




EUROCONTROL                                                                                                                  Page 16

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 Figure 1: Illustration of the CREDOS WTSSAV determined by the wind monitoring capabilities of the
 airport. Inside the WTSSAV, when CREDOS may be applied, the wake turbulence separation minima
            may be suspended. Outside, the standard ICAO wake turbulence minima apply.




3.2.1. Minimum reduced spacing
        Inside the WTSSAV, when the CREDOS wind level is reached, the wake turbulence separation
        may be suspended. Outside, since the wind conditions cannot be monitored, the ICAO standard
        wake turbulence separation minima apply. In this concept, it has been assumed that the safest
        way of consistently achieving correct spacing according to all ICAO rules when transiting out of
        the WTSSAV would be to apply ICAO wake turbulence radar separation even if visual,
        horizontal or vertical separation could also be achieved.

        Consequently, the spacing between two consecutive departures, when CREDOS operations
        apply (i.e. when the wake turbulence separation may be suspended inside the WTSSAV) has to
        be set so that a transition:

                  from no wake turbulence separations, when inside the WTSSAV,

                  to ICAO wake turbulence radar separation minima, when outside,

        is properly achieved.

        This transition constraint leads to the conclusion that CREDOS suspension of wake turbulence
        separation minima does not directly imply that applicable spacings between consecutive
        departures are equal to the minimum radar separation (i.e. 3.0 NM). The methodology used to
        determine the suitable reduced spacing is further described in section 3.2.3.



EUROCONTROL                                                                                                                  Page 17

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          CREDOS spacing is determined in a two-step process:

                   determination of the WTSSAV size;

                   determination of CREDOS spacing.

          The suitable spacing between two consecutive departures in CREDOS operations may be
          expressed in terms of a time-based minimum (as it is mainly applied today) or in terms of a
          distance-based minimum. At this stage, it is considered to be a local responsibility to determine
          the best spacing means, according to specific local infrastructure, procedures, constraints,
          requirements and expectations.

          It is worth noting that the suitable reduced spacing is defined on the basis of the pre-defined
          crosswind threshold and the pre-defined size of the WTSSAV. It will not therefore fluctuate with
          variation of the crosswind component. When the crosswind component meets the pre-defined
          requirement, CREDOS reduced spacing may be applied. When below the defined crosswind
          component threshold, CREDOS may not be applied.


3.2.2. Determination of the size of the WTSSAV
          It has been concluded that CREDOS application requires monitoring of the wind to determine
          whether the crosswind component reaches the pre-defined threshold. The range of the Wake
          Turbulence Separations Suspension Airspace Volume is limited by the technical capability to
          evaluate, with sufficient accuracy for CREDOS application 4 , the wind condition prevailing in the
          area surrounding the departure path. Most of the time, such technical issues will limit the height
          of the WTSSAV, which then also defines the height at which the transition from CREDOS
          reduced spacing to ICAO standard wake turbulence separations has to be obtained.

          Of course, the higher the vertical size of the WTSSAV, the more time will be available to
          perform the transition (including for instance the pull-away effect where aircraft spacing
          increases over time). Consequently, with respect to the transition constraint the higher the
          vertical size of the WTSSAV, the shorter the CREDOS reduced spacing can be, increasing the
          benefits of CREDOS application.

          Laterally, besides the limitation due to the range of the wind assessment equipment, the size of
          the WTSSAV is mainly determined by the required width of the wake turbulence safety corridor
          around the path of the departing aircraft. The width of the corridor is established on the basis of
          safety arguments, taking into account the range of the wind assessment equipment (which
          should not constitute a limitation), the capability of the aircraft to accurately navigate their
          departure paths, and the SIDs layout.

          In conclusion, the size of the WTSSAV has to be defined locally on the basis of local wind
          monitoring means (height of the airspace volume), of the aircraft’s accuracy to fly the local
          departure paths (width of the airspace volume) and of the structure of the SIDs.

          Annex A.2 presents an example of the determination of the WTSSAV size.



4
    It is a local responsibility to define, on the basis of local data collection, the minimum wind monitoring accuracy required for CREDOS

application

EUROCONTROL                                                                                                                  Page 18

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3.2.3. Determination of the CREDOS spacing
        Once the Wake Turbulence Separations Suspension Airspace Volume has been sized, the
        suitable CREDOS spacing can be determined. It is worth noting that this spacing is not
        determined each time the concept is applied. On the basis of the weather measurement data
        collected, the size of the WTSSAV and of aircraft and traffic mix performances, the suitable
        CREDOS spacing is determined prior to deployment of the concept.

        CREDOS spacing is the minimum longitudinal position difference that must exist between two
        departing aircraft at the time the take-off clearance is issued to the second aircraft in cases
        where the wake turbulence separation minima may be suspended. The position difference is
        referenced to the leading aircraft and may be expressed in time elapsed or distance covered (or
        both) from start of the take-off roll. Each of these two methods has advantages and drawbacks,
        and a local evaluation of both is required to select the more appropriate one.

        It is important to stress that the CREDOS spacing scheme is to be considered as advice and
        support, given to the runway controller when determining aircraft separation for departures.

        What is described in this section is the methodology that guides the determination of the
        suitable spacing minimum regardless of the spacing method.

        When applicable, the CREDOS suspension of wake turbulence separation leads to spacing
        lower than that resulting from the use of wake turbulence separation minima, but never less
        than the corresponding minima applicable when an ATS surveillance service is provided in
        TMAs (usually 3.0 NM, corresponding approximately to a 60-second time separation).

        As described above, the time needed for the crosswind to blow the vortices clear of the
        succeeding aircraft’s departure path, and the requirement to obtain the ICAO wake turbulence
        separation when this follower aircraft exits the WTSSAV have to be taken into account.

        So the CREDOS aircraft wake turbulence separation reduction, when enabled by the crosswind
        component, is determined by all of the following three conditions:

                  the time between two departures, when the wake turbulence separation minima are
                   suspended, has to be sufficient to ensure that the wake turbulence is transported out of
                   the departure path;

                  consecutive departing aircraft always have to be separated by at least the applicable
                   ATS surveillance system based separation minimum (usually 3.0 NM);

                  transition from CREDOS spacing to ICAO standard wake turbulence separation has to
                   be obtained prior to the point at which the succeeding aircraft reaches the upper
                   boundary of the WTSSAV.

        Of course, to be considered suitable, the CREDOS reduced spacing has to satisfy each of these
        constraints. This can be ensured by the use of a general iterative decision-making process
        illustrated by the decision tree in Figure 2.

        During this iterative process, any CREDOS reduced spacing candidate is checked against each
        of the three constraining factors to assess whether each constraint is satisfied or not. If a
        criterion is not met, the spacing has to be increased. The output of the process is a spacing that
        accommodates all three constraining factors.


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        An example of this process is developed in annex A.3.




       Figure 2: Decision-making process for determining the suitable CREDOS reduced spacing.


        To summarize, prior to deployment of CREDOS, it is required to locally size the airspace
        volume within which the suspension of the wake turbulence separation minima will be allowed
        (see section 3.2.2). Then, on the basis of the WTSSAV size, the CREDOS spacing is computed
        once, using the iterative process depicted here.


3.2.4. SID considerations
        The proposed concept is based on the lateral transport of the wake turbulence due to the
        crosswind. As a consequence, attention has to be paid to the respective SIDs of the
        consecutive departing aircraft. The suspension of the wake turbulence separation minima may
        be applied only for the succeeding aircraft when on the same or an upwind SID by reference to
        the preceding heavier aircraft.

        Applying CREDOS operations when the follower aircraft is on a downwind SID would lead to a
        situation where the follower flies in the direction where the wake turbulence generated by the
        leader is transported, which is not a safe situation.

        Figure 1 (page 17) shows a case for which if the second aircraft is on SID 2 or SID 3, the
        suspension of the wake turbulence separation may be applied. If the follower is assigned on
        SID 1 which is upwind by reference to the leader SID (i.e. SID 2), CREDOS suspension of


EUROCONTROL                                                                                                                  Page 20

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        separation may not be applied. Figure 3 below illustrates a case for which the proposed
        suspension of the wake turbulence separations may be applied only if the following aircraft is on
        the same SID as the leader (i.e. SID 3).




  Figure 3: SID consideration scheme. In this case, if the second aircraft is on the same SID as the
leader (i.e. SID3), CREDOS is allowed. If the second is on any other SID (both downwind) CREDOS is
                     not allowed. Note that there are no upwind SIDs in the example.


        In the context of CREDOS, the suspension of wake turbulence separation minima concerns only
        the runway and the first part of the climb phase. Thus, it should be possible to unambiguously
        identify upwind and downwind SIDs, even in the case of sharp turns shortly after the end of the
        runway. In any case, if upwind and downwind SIDs cannot be clearly determined, the proposed
        concept may not be applied for those particular SIDs.

        In order to support the runway controller in determining whether or not the SID of the follower
        aircraft is upwind, advisory tools and procedures should be developed if necessary.

        As a result of these considerations, any actual application of CREDOS suspension of the wake
        turbulence separation minima has to be determined per airport, per runway, and also per
        departing aircraft pair, taking into account the respective SIDs of the aircraft.


3.2.5. CREDOS departure process (example)
        Assuming a MEDIUM aircraft departing after a HEAVY aircraft, both on the same SID, and
        assuming also that the wind conditions are such that the wake turbulence separation may be
        suspended, the CREDOS departure process would then be the following:

EUROCONTROL                                                                                                                  Page 21

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                  clearance issued to the HEAVY aircraft;

                  HEAVY aircraft starts to roll and then takes off;

                  once the CREDOS spacing minimum is obtained, the clearance for take-off can be
                   issued to the MEDIUM aircraft;
                  when cleared, the MEDIUM starts to roll and then takes off;
                  finally, the MEDIUM reaches the boundary of the WTSSAV, where the wake turbulence
                   separation minima must be achieved (in this case 5 NM).


3.2.6. Application of CREDOS spacing
        The application of CREDOS wake turbulence separation minima suspension covers the initial
        climb segment up to the top of the WTSSAV (see section 3.2.2), where the transition to the
        ICAO wake turbulence separation minima is to be obtained.

        Outside the WTSSAV, the ICAO wake turbulence separation minima apply.




EUROCONTROL                                                                                                                  Page 22

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3.3. CREDOS OPERATION IN THE CURRENT ATC/ATM ENVIRONMENT

3.3.1. Definition of CREDOS roles and procedures
        This section describes the proposed roles and procedures for a crosswind departure concept.
        Further details can be found in references [7], [15], [22] and Annex B. There are local variations
        in methodology, rating, roles and/or responsibilities. The concept description aims to achieve a
        generic level rather than a more detailed, site-dependent level. The roles and tasks are
        described as being part of a future environment when the concept is widely known and
        accepted by controllers and flight crews.

        As different towers have somewhat different roles and positions, the following chart (see Figure
        4) describes the phases of flight and the general high-level controller and flight crew
        responsibilities (green boxes) and actions (white boxes) for each phase of flight.

        For a specific flight crew there is a clear logical flow during the aircraft departure, but from the
        controller's point of view there is no such work flow. For each controller position/role, many
        simultaneous flights in different phases of the departure process are incorporated into the
        controller task. In the chart, this is shown by not linking one event in the flight progress to the
        next one.

        The grey diamond shapes indicate action needed from a controller because of a request
        initiated by the flight crew. In the other cases the action is initiated by the controller.

        Arrows leading to a "no" box will change to "yes" when the constraining factors have been
        removed. For instance, depending on how an aircraft is parked, push-back is sometimes
        needed but not always. Start-up clearance must always be requested but does not have to be
        commenced immediately after the request. Local procedures can vary and start-up can be
        requested before push-back, but to commence after push-back.




EUROCONTROL                                                                                                                  Page 23

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                                                               Figure 4: Nominal departure flight decision flow (without CREDOS).

EUROCONTROL                                                                                                                                      Page 24

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        Compared to current roles and procedures, the major change introduced by the proposed
        concept is that when CREDOS operations apply, it is presumed that it is the runway controller
        who is responsible for ensuring aircraft separation after departure, This includes the monitoring
        of the transition from CREDOS reduced spacing to the ICAO standard wake turbulence
        distance separations.

        To illustrate the description of the roles and procedure, the following scenario is used:

              A MEDIUM aircraft will follow the same track/SID as a HEAVY or an upwind track/SID and
              the 2-minute rule as well as the 5 NM rule can be suspended.


3.3.1.1. Tower and approach supervisors
        The supervisors in the tower and in approach are coordinating tactical decisions about landing
        and departure rates, constraints and runway changes. In the tower the supervisor is the main
        role responsible for obtaining and monitoring weather forecast services.

        Consequently, it is proposed that the tower supervisor, in coordination with the approach control
        supervisor, would be the only role responsible for the activation/deactivation (see terminology in
        section 1.4) of the CREDOS system. It has been concluded that in the case of urgent matters,
        other controller roles would also have the capability to deactivate CREDOS.

        The activation decision is based on traffic demand, traffic mix and the foreseen length and
        certainty of a prevailing capacity change. It is also based on ‘availability’ of the CREDOS
        system. When ‘not available’, the system cannot be activated. Finally, the supervisor assesses
        the potential benefits of the use of CREDOS suspension of the wake turbulence separation in
        terms of throughput increase.

        The tower supervisor carries out the following steps to activate CREDOS:

                  informs the runway controller that CREDOS will be activated;

                  presses the CREDOS activation button;

                  informs clearance delivery, departure controller and ground controller that CREDOS is
                   active;

                  ensures that CREDOS in-use information is included in ATIS broadcasts (if available).


3.3.1.2. DMAN
        DMAN is not required for the CREDOS concept to work. Since CREDOS is applied case-by-
        case only, no changes in the forecast runway capacity will be determined or expressed or put
        into any runway sequence management or flow management system. The concept will then just
        ease peak queuing at the runway and improve punctuality through a temporary increase in
        runway throughput.

        Nonetheless, if a period of time with forecast stable crosswind conditions can be identified, an
        opportunity arises to declare for this time period an increase in runway capacity. Depending on
        the length of this period, and if a departure peak can be foreseen, this higher capacity could
        then be fed into a DMAN system and could also be sent to CFMU.



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         Regardless of whether a DMAN system exists or not the ground controller would then try to
         deliver a continuous flow of traffic to the runway so that the benefit of this higher capacity can
         be fully exploited.

         On the other hand CREDOS operations imply that new requirements would be put on a DMAN
         system. DMAN would have to be able to temporarily overrule the weight category separation to
         allow CREDOS suspension of wake turbulence separations for certain aircraft pairs. It would
         also have to be able to determine whenever a SID combination is conducive to suspending the
         wake turbulence separation minima, depending on the direction of the wind (right or left).


3.3.1.3. Clearance delivery

         The CREDOS concept affects the Flight Plan and clearance delivery position/role very little.
         When CREDOS is in use, this role should make sure that MEDIUM and LIGHT departing
         aircraft are aware of CREDOS separation suspension. In a non-automatic environment this
         position must also consider whether or not consecutive aircraft are on the same, or an upwind,
         SID. The flight crew must be made aware that CREDOS is in use by AIP. Information on
         CREDOS operations currently in use must be provided to the flight crew prior to push-back or
         taxiing out for take-off. This can be provided by ATIS broadcast and checked by clearance
         delivery.


         Proposed phraseology example (with respect to the proposed scenario) 5 :

              Clearance delivery to flight crew:

                 “Anticipate suspended wake turbulence separation behind HEAVY (or MEDIUM)
                 aircraft”.

              Flight crew:

                 “Roger” or

                 “Unable to comply with reduced separation”

         When flight crew reports that it is unable to comply with a reduced separation, this should be
         noted by clearance delivery and the information must be transferred to ground and Runway
         controllers.

         If this position/role also delivers start-up clearance and a Departure Management system
         (DMAN) is in place, the CREDOS spacing can be calculated and therefore lead to changes in
         the pre-determined start-up sequence for departures (based on the respective wake turbulence
         categories and the respective SIDs of the aircraft).

         The HMI in the working position should reflect the CREDOS system availability and activation
         status.




5
    Note that the phraseology proposed in this document is to be considered as an example only. The proposed CREDOS phraseology

has not been coordinated with any authority such as ICAO or national CAAs.

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        The clearance delivery position, as all other positions, could deactivate CREDOS if necessary
        (e.g. emergency, request from other controller position). Responsibility for activating CREDOS
        again remains the supervisor’s.


3.3.1.4. Ground controller
        The ground controller is responsible for executing the sequencing of departing traffic. This task
        is based on knowledge about CFMU-issued constraints per aircraft (e.g., Calculated Take-Off
        Times), present runway capacity and configuration, and local constraining factors such as
        closed taxiways or other traffic. The ground controller must know when CREDOS is activated in
        order to integrate the potential benefit in the sequence preparation work.

        If suspended wake turbulence separations are possible between pairs of aircraft on assigned
        specified SIDs, the ground controller can optimize the sequence as far as possible, taking
        account of the opportunities to apply CREDOS operations. This preparation remains a purely
        tactical action, as other sequence prioritising also takes place during the taxiing out phase.
        Normally the ground controller builds the sequence of aircraft on a ‘first-come first-served’
        principle when aircraft request start-up, push-back and taxi clearance. The closer the aircraft
        gets to the holding point of the assigned runway, the more all criteria for an optimal sequence
        will be taken into account. Aircraft with Calculated Take-Off Time (CTOT) are considered, as
        well as the planned route and altitude after departure. Furthermore, aircraft performance and
        aircraft wake turbulence category is information that affects the departure sequence planning.
        The sequence of departing aircraft is continuously monitored, changed and updated by the
        ground controller.

        When aircraft get closer to the runway, the ground controller can often choose between two or
        more holding positions (multiple line-up) for departing aircraft, depending on the local layout.
        This is the moment when the CREDOS benefits can most easily be exploited. Again, if
        CREDOS can be used for certain SIDs upwind of preceding aircraft, this will also be considered.
        The runway controller is, however, the last controller during this part of the flight to decide and
        modify the actual departure sequence and spacing.

        The flight crew must be informed that CREDOS is being applied by AIP and ATIS information.
        The flight crew might report that they are unable to comply with suspended separation and this
        should then be noted by the ground controller and be transferred to runway controller. The flight
        progress strips of such aircraft are marked manually or electronically, as applicable.

        The ground controller must have the same display possibilities at the working position as the
        runway controller. The CREDOS ‘available’ and ‘active’ status, the GO/NO-GO display as well
        as the interface for determining upwind SID application must be shown (see runway controller
        description). The ground position, as all other positions, can deactivate CREDOS if necessary
        (such as in emergencies or at the request of another controller position). Responsibility for
        activating CREDOS remains the supervisor’s.

3.3.1.5. Runway controller
        In a segregated departure mode, the runway controller is responsible for applying a safe and
        efficient departure flow. The runway controller has to consider runway separation rules and local



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          spacing methodology in order to deliver aircraft to the departure radar controller. When applying
          the 2-minute rule, the runway controller can use different methods.

          Before entering into the details of the runway controller roles and procedures in CREDOS
          operations, it is worth recalling that, in the proposed concept, it is assumed that the runway
          controller has a radar display and has the ability to monitor departing aircraft in order to deliver
          traffic to the departure controller in the approach sector with the appropriate spacing. runway
          controllers use a set of separations in their daily work. They are called runway separations. In
          addition to these separation rules, the runway controller also provides spacing between
          departures in order to obtain the required radar separation after departure. The local procedures
          for this can vary at different airports.

          The runway controller is continuously informed about the current weather conditions and the
          availability of CREDOS and must have a GO/NO-GO interface displayed in the working position,
          making it possible to determine for each CREDOS-applicable departure pair whether a
          suspension of wake turbulence can be applied or not.

          The runway controller will also need to determine whether or not the SID of the follower aircraft
          is suitable for CREDOS suspension. In order to help the controller, a suitable support tool 6
          indicating useable SIDs should be available if needed. A safe SID is the same SID or an upwind
          SID by reference to that of the preceding heavier aircraft.

          Prior to take-off, the runway controller informs each aircraft, in the case of CREDOS being in
          operation, whether departure separations suspension can be authorised (sufficient crosswind
          and suitable track/SID by reference to the leader). Information on suspension must be provided
          to the aircraft about to take-off.


          Proposed phraseology examples (with respect to the proposed scenario):

               Runway controller to departing flight crew while aircraft is lining up or when it is in the take-
               off position:

                 “Wind is 360 degrees, 20 knots. Wake turbulence separation suspended behind
                 HEAVY (or MEDIUM) aircraft, cleared for take-off”.

               Flight crew:

                 “Roger, cleared for take-off”.




6
    CREDOS HMI and support tools are described in section 3.3.4.

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        In cases where the CREDOS system is already in ‘available’ and ‘active’ mode, the sequence of
        operations for the runway controller can be described as follows:

                  the runway controller notes that the CREDOS status indicator GO/NO-GO indicates that
                   wake turbulence separation can be suspended between departures, if all other
                   CREDOS criteria (such as SID geometry) are met;

                  take-off clearance is issued to the leading aircraft in the heavier-lighter pair and the
                   take-off and initial climb is observed as usual;

                  the following aircraft is cleared to line up and wait. The runway controller assumes that
                   the aircraft has been informed of CREDOS use and has not rejected the suspension of
                   wake turbulence separation;

                  the runway controller ascertains that the SIDs of the aircraft pair are such that the wake
                   turbulence separation minima may be suspended. If this is not the case, ICAO standard
                   wake turbulence separation is applied and the rest of the procedure described here is
                   not applicable;

                  the runway controller informs the aircraft just before line-up or when it is in the take-off
                   position that wake turbulence separation for them is being suspended.

                  the flight crew accepts the suspension and the runway controller applies the appropriate
                   CREDOS spacing. The take-off clearance is issued when the controller determines that
                   all the spacing criteria are met;

                  the aircraft is transferred to the departure controller in accordance with local
                   procedures.

        The runway controller keeps the ability to modify the sequence prepared by the ground
        controller. One objective is then to minimise the average delay over the whole population of
        aircraft in the queue.

        If information regarding significant changes in the meteorological conditions in the take-off or
        climb-out is received from other aircraft or any other reliable source, it must be transmitted to
        the departing aircraft without delay, especially if this information could impact the safety of the
        CREDOS departure.

        In the case of a flight crew reporting a serious wake vortex encounter or a significant change in
        wind direction or any other CREDOS-critical conditions, any controller role (runway or
        departure) who receives such information must also be able to deactivate CREDOS operations
        if necessary.




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3.3.1.6. Departure controller in the TMA
          The management of the traffic transferred to the departure controller using CREDOS operations
          is not significantly different as all aircraft are still delivered applying standard wake turbulence
          separation minima.

          Depending on the weather conditions and the local responsibilities and procedures for
          separations applied by the tower and departure controller, the transfer point of control and radio
          frequency can vary.

          If information regarding significant changes in the meteorological 7 conditions in the take-off or
          climb-out is received from other aircraft, it must be transmitted to the departing aircraft without
          delay, especially if this information could impact the safety of the CREDOS departure. Such
          information should also immediately be transferred to the runway controller.

          Since departure controllers must be able to deactivate CREDOS if necessary (for example in
          emergencies or following a request from another controller position), their working position must
          have the same HMI as that of the runway controller.


3.3.1.7. Flight crews
          Today flight crews do not expect controllers to apply shorter spacing than the minimum
          departure separation according to the ICAO wake turbulence rules. Common practice in
          departure operations for the flight crew is to time the interval between when the preceding
          aircraft (e.g. HEAVY) starts its take-off roll (or when it becomes airborne) and the time to
          commence the following take-off roll (e.g. 2 minutes).This timing is of course also done by the
          runway controller. In this way the flight crew can cross-check compliance with the ICAO wake
          turbulence rules. In general the flight crew is not responsible for the separation, but is always
          ultimately responsible for the safety of the aircraft.

          A flight crew can sometimes decide to use a longer spacing than the one proposed by the
          controller if it is considered appropriate. In this case, the flight crew is expected to report this
          delay to the runway controller.

          Flight crews must at all times be aware of the suspension of wake turbulence separation. This
          must be published on ATIS. Once the CREDOS concept is well established, it would be enough
          to publish the procedures in AIP and then broadcast on ATIS when it is actually in use. Flight
          crews must report to tower if unable to comply with the suspended separation behind heavier
          aircraft.

          In cases where CREDOS operations have just been activated (i.e. not yet captured on ATIS) it
          will also be necessary to inform flight crews on the frequency while taxiing out for departure.
          The ground controller and runway controller will then address this information only to those
          aircraft that are expected to be subject to a CREDOS clearance.




7
    Meteorological conditions include the crosswind or significant weather changes such as thunderstorms or wind shear.

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3.3.1.8. Actors
        This section introduces the human actors involved in CREDOS operations.


             Actor                          Current Responsibility                        Specific/additional role in CREDOS
 Tower ATC supervisor              Has overall responsibility for the                   Decides when to activate the CREDOS
 (SUP)                             planning of the tower operation.                     system based on forecast, nowcast and
                                   Monitors operations. Decides on                      wind information as well as traffic
                                   arrival and departure rates. Proposes                demand, traffic mix and runway
                                   runway configuration. Gives                          configuration.
                                   permission for maintenance, etc.
 Runway controller                 In charge of take-off phases, including Puts in place and monitors safe
 (TWR)                             runway and radar separation.            separations and efficient spacing and
                                                                           sequence using the CREDOS
                                                                           suspension of wake turbulence
                                                                           separations. Receives and disseminates
                                                                           CREDOS critical wake vortex and
                                                                           weather information.
 Ground controller                 Gives start-up and push-back                         Uses DMAN (or similar) information
 (GND)                             clearance. Sequences arrivals and                    based on CREDOS or adjusts manually
                                   departures and manages queuing                       to the CREDOS capacity and
                                   according to the runway and stand                    sequencing opportunities.
                                   capacity/availability.
 Clearance delivery                Reads clearances to departing traffic.               Informs departures that CREDOS is in
 (CND)                                                                                  use.
 Departure radar                   Separates safely aircraft on radar                   Monitors CREDOS availability and
 controller (DEP)                  after departure. Manages an efficient                application per flight. Receives and
                                   flow of traffic out of the runway into               disseminates CREDOS-critical wake
                                   the en-route or TMA sectors.                         vortex and weather information.
 Flight crew                       Navigates aircraft safely                            Is aware of CREDOS operation and the
                                                                                        suspension of wake turbulence
                                                                                        separations. Reports CREDOS-critical
                                                                                        information.
 TMA supervisor                    Plans and monitors operation of the                  Is informed about CREDOS activation.
                                   TMA

                   Table 2: Actors and changes to the role when using the CREDOS concept




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3.3.2. Wind strength and direction
          The CREDOS concept is based on the lateral transport by crosswind of the wake turbulence
          generated by preceding aircraft, out of the departing track of the following aircraft. The
          suspension of the wake turbulence separation minima is subject to being able to observe a
          crosswind which is sufficient to ensure that the wake turbulence is transported out of the
          departing track.


          Crosswind component threshold

          ‘Sufficient’ crosswind is defined as the standard minimum crosswind measured with the airport
          sensors in order to ensure that the probability of wake turbulence persisting within the
          suspension airspace volume when aircraft become airborne in a suspended departure
          separation mode is acceptably low 8 . In order to mitigate flickering ‘GO’/’NO-GO’, forecasts and
          algorithms must be used that capture the stability of the wind.


          CREDOS wind level

          A set of conditions, determined by the local ATS authority, all of which must be satisfied for
          CREDOS spacing to be applicable on a given runway between a given pair of departing aircraft.
          Conditions include the crosswind component, but could also include wind speed and direction
          steadiness or significant weather changes such as thunderstorms or wind shear. Specific
          CREDOS levels may be defined for activating/deactivating CREDOS in order to ensure safe
          operation and avoid flickering GO/NO-GO indication.

          For efficient use of the concept, it would also be beneficial to be able to apply the concept for
          long periods of time. It would therefore be useful for planning purposes to have weather
          forecasts which establish periods for the application of CREDOS operations.


          Aerodrome wind monitoring capabilities

          The first means of monitoring the wind is measuring it. Wind can be measured on the
          aerodrome but the accuracy of measurement decreases with distance from the aerodrome. The
          higher above, or further from, the aerodrome the wind is measured, the less accurate is the
          measurement. Additional sensors can help but costs set a limit to what can reasonably be done.
          In addition to wind measurement, wind nowcasting and/or forecasting can constitute a second
          means of monitoring.

          It is clear that the capability to accurately monitor the crosswind conditions (and hence to use
          the actual presence of crosswind to build confidence in vortices being blown out of the way)
          limits the volume of airspace in which the reduced spacing can in fact be applied.

          Depending on the measuring and nowcasting/forecasting capability actually available,
          aerodromes using CREDOS will have to designate a volume of airspace around and beyond the
          runway concerned in which the reduced spacing can be applied. The volume must have


8
    The acceptable probability level is to be determined by a local safety case. The outcome of the generic safety case (see ) and of the

tasks performed in the WP3 of the project (see ) would support the local safety case.

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        assured wind measurements and must contain, to the extent required and with an appropriate
        buffer, the tracks of departing aircraft.


3.3.3. CREDOS system status
        It has been seen that the CREDOS system can experience various statuses such as
        ‘available’/’not available’ or ‘active’/’not active’, etc. This section describes the meaning of the
        different statuses of CREDOS.

        The suspension of the wake turbulence separation minima for a particular aircraft pair requires
        that the CREDOS system be ‘available‘, ‘activated’ and that the CREDOS status indicator
        shows GO. The hierarchic organisation of these statuses is represented in Figure 5.




                       Figure 5: Scheme of the hierarchy of the different CREDOS statuses.


3.3.3.1. CREDOS ‘available’/’not available’
        CREDOS ‘available’/’not available’ reflects the status of CREDOS at system level.

        CREDOS availability indicates that all the elements of the CREDOS system are working
        properly, including all required data sources, computers, HMI display, etc.




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        CREDOS availability is a prerequisite for the system to be activated. Since activation is a task
        for the tower supervisor, CREDOS availability is usually indicated only at the designated
        supervisor position.


3.3.3.2. CREDOS ‘active’/’non-active’
        CREDOS system status that reflects when CREDOS is in operation. Once activated by the
        tower supervisor, CREDOS ‘active’ status is displayed on the appropriate controller position
        HMI (see section 3.3.4). CREDOS operations may be applied only when CREDOS is ‘active’.
        When ‘non-active’, standard operations are applied.


        CREDOS activation

        Activation requires the CREDOS system to be ‘available’. Responsibility for activating the
        CREDOS system falls to the tower supervisor (possibly in coordination with the approach
        control supervisor). CREDOS will be activated when additional runway throughput is desirable
        and the actual and forecast crosswind conditions support the suspension of wake turbulence
        separation. When the supervisor activates CREDOS, the ‘active’ status is shown on the HMI of
        the appropriate controller working positions (see section 3.3.4 for details on the HMI).


        CREDOS deactivation

        The deactivation of the CREDOS system is also the responsibility of the tower supervisor.
        However, for safety reasons, the clearance delivery, the runway or the departure controller may
        also deactivate CREDOS when urgent, unexpected circumstances arise (or when the tower
        supervisor is temporarily not available). In the context of CREDOS operations, unexpected
        circumstances could arise in the form of unstable wind conditions, sudden severe weather
        conditions, surveillance system failure or other system failure resulting in a lack of information
        essential for CREDOS operation, sector overload, etc.

        The exact procedure to be followed is dependent on the local working arrangements and the
        particular CREDOS implementation. In all cases, however, the application of CREDOS spacing
        must be terminated immediately upon CREDOS deactivation. The user interface needs to signal
        clearly that deactivation has taken place.

        CREDOS may be implemented with an automatic shut-down capability that deactivates
        CREDOS in the event of a critical system failure. The tower supervisor, clearance delivery and
        the runway, departure and ground controllers must always be informed of such deactivation in a
        clearly recognizable way. Procedures must also be in place to enable continued proper
        management of traffic when automatic CREDOS deactivation occurs.


3.3.3.3. CREDOS ‘GO’/’NO-GO’
        ‘GO’/’NO-GO’ is the status of the CREDOS HMI indicator that will indicate whether or not
        CREDOS operations can be applied for a specific following aircraft. This solution can be simple
        and solely based on meteorological data (see footnote 7, page 30) input, or more advanced
        taking into account specific flight plan data and radar data in addition to the crosswind data.



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        The stability of ‘GO’/’NO-GO’ advice is important and therefore forecasts and algorithms must
        be used that capture the stability of the wind in order to mitigate flickering advisory.

        The procedure described below is the simplest solution where the ‘GO’/’NO-GO’ status is based
        on crosswind data only.


3.3.4. CREDOS HMI and support tools
        As mentioned above and in the Human Factor Case report [18], it is recommended, that
        dedicated HMI and tools be developed to support the task of controllers when applying
        CREDOS operations.

        Since the design of these HMI and tools depends heavily on local constraints and
        infrastructures, what is described in this section is to be considered as one proposed generic
        version.

        HMI

        The CREDOS suspension of the wake turbulence separation minima requires specific
        information to be presented to the controllers. Indeed, controllers must be clearly advised on the
        status of the CREDOS system (see section 3.3.3) and on whether or not CREDOS criteria to
        suspend the wake turbulence separations are met.

        For the proposed HMI, when referring to CREDOS criteria, only crosswind conditions are
        accounted for (CREDOS wind level met or not). More advanced solutions may be developed
        that include the respective wake turbulence category of the aircraft pair, the SID geometry, etc.

        In this version of the HMI solution, two columns dedicated to CREDOS have been added in the
        meteorological information panel:

                  an ‘xwind’ column that contains the value of the crosswind component;

                  a ‘credos’ column that shows the CREDOS status indicator.

        When the CREDOS system is ‘not available’, the CREDOS status indicator of all working
        positions is empty (Figure 6).




                      Figure 6: Example of a CREDOS HMI when CREDOS is ‘not available’.


        When CREDOS system becomes ‘available’ but still ‘not active’, the CREDOS status indicator
        of clearance delivery, the runway controller, the departure controller and the ground controller
        changes to -- . Once ‘available’, the CREDOS system may be ‘activated’ by the tower
        supervisor (via a dedicated HMI, see Figure 7).




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            Figure 7: Example of a CREDOS tower supervisor HMI when CREDOS is ‘not active’.


        As expressed in the previous section, CREDOS activation is the responsibility of the tower
        supervisor, therefore other working positions do not have the activation capability on their local
        HMI, see Figure 8.




        Figure 8: Example of a CREDOS HMI when CREDOS is ‘not active’ (all working positions).


        On CREDOS activation, the CREDOS status indicator changes to either GO or XX (symbolising
        NO-GO indication).

        GO (Figure 9) means that the system has been activated and the CREDOS wind level is met.
        CREDOS spacing may be applied for the next departing aircraft but only if SID geometry
        permits.




  Figure 9: Example of a CREDOS HMI when CREDOS is ‘active’ and the CREDOS wind level is met.


        XX (Figure 10), that stands for NO-GO, means that the system has been activated but the
        CREDOS wind level is not met. Hence CREDOS spacing must not be applied.




  Figure 10: Example of a CREDOS HMI when CREDOS is ‘active’ and the CREDOS wind level is not
                                            met.



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        On CREDOS deactivation, the CREDOS status indicator of clearance delivery, the runway
        controller, the departure controller and the ground controller comes back to -- (Figure 7).


        Support tools

        When the CREDOS status indicator shows GO (Figure 9), it means that CREDOS spacing may
        be applied for the next departing aircraft, but only if SID geometry permits. To help controllers in
        assessing whether the respective SIDs of the aircraft allow suspension of the wake turbulence
        separation in case of GO, it is recommended that a supplementary support tool be developed.

        In a more advanced solution, this could be incorporated into the HMI solution to be part of the
        CREDOS status indicator. In such a case, GO would mean that the crosswind is above the
        CREDOS wind level and that the SID geometry permits suspension of the wake turbulence
        separation.

        A simpler solution for the SID support tool could for instance be a schematic map of the SID and
        a coloured table, by runway, for each crosswind direction (see example in Figure 11).




  Figure 11: Example of a support tool developed to aid controllers to determine whether or not SID
  geometry permits the suspension of the wake turbulence separation in case of GO (from CREDOS
                                real-time simulations – session 2).


        Assuming, as an example, that the crosswind is blowing from the right of the runway, this look-
        up table then shows that when the leader is on SID SOUTH 3A, CREDOS spacing may be


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        applied if the following aircraft is either on SOUTH 3A or on WESTY 3A (green entries in the
        table). On the contrary, if the follower is on EASTY 1A, the red table entry indicates that
        CREDOS suspension of the wake turbulence separation must not be applied.



3.3.5. What is needed before local implantation?
        At this stage of the concept development, the following activities have been identified as needed
        prior local implementation.

        Data collection

                  wind profiling and modelling, wake signatures and behaviour;

                  current aircraft performances per aircraft type and SID in terms of climb rate and
                   navigation performance;

                  validation against existing data sets from other airports;



        Benefits case that takes into consideration:

                  local wind conditions over the day and over the year (i.e. how often is the CREDOS
                   wind level met);

                  runway usage, traffic peaks, and mix of aircraft types;

                  constraints because of SID layout and mix, constraint because of runway crossings
                   (when HEAVY departs the 2 min sep is often used for crossings).




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3.3.6. CREDOS System requirement
        See separate document D4-1 “Operational and System Requirements” [15].

3.3.7. CREDOS User Requirement
        See separate document D4-1 “Operational and System Requirements” [15].

3.3.8. CREDOS Operational Requirement
        See separate document D4-1 “Operational and System Requirements” [15].




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4. EXPECTED BENEFITS OF THE CREDOS CONCEPT
        In today’s operations, the capacity of large airports is constrained inter alia by the application of
        wake turbulence separation minima. The suspension of these original, static and sometimes
        over-conservative separation minima, as proposed in the CREDOS concept, would lead to a
        temporary increase of departure runway throughput with a view to reducing departure delays
        and/or absorbing capacity peaks.

        According to ICAO wake turbulence rules, the departure runway throughput increase brought by
        the CREDOS concept occurs only when an aircraft in a lighter wake turbulence category directly
        follows a heavier one and the CREDOS wind level is met. So, the potential for reducing the
        spacing is to be found only in cases of:

                  MEDIUM or LIGHT behind HEAVY (today 2-minute or 5/6 NM, see section 2.2);

                  LIGHT behind MEDIUM (today also 2-minute or 5 NM).

        Ideally, the suspension of the wake turbulence separation minima leads to an aircraft spacing
        between consecutive departure of 60 seconds while maintaining minimum 3 NM (for following
        on a diverging upwind SID) radar separation and around 100 seconds while maintaining 5 NM
        radar separation (for aircraft following on the same or downwind SID and where 5 NM miles has
        to be applied either because of en-route separations or because of 5 NM wake turbulence
        separation required at a later phase than initial climb phase).

        In practice, CREDOS spacing has to account for constraints other than the fact that aircraft may
        never be closer to each other than the applicable ATS surveillance system based separation
        minimum. Indeed, it has been established that the time separation between two departures has
        to be sufficient to ensure that the vortices have been blown out of the departing track prior to the
        second aircraft being airborne and also that the spacing between the two aircraft must be such
        that the establishment of ICAO standard wake turbulence separation minima is possible when
        the second aircraft exits the WTSSAV.

        Nevertheless, the CREDOS suspension of wake turbulence separation leads to spacing lower
        than that resulting from the use of wake turbulence separation minima.

        The major benefits are to be achieved during peak periods or when queuing creates delays of
        departing traffic at the runway. In a queuing situation, the benefit for aircraft further down the
        queue can add up to a substantial reduction of waiting time, even if the gain experienced by
        individual aircraft is limited. This translates into improved punctuality (see CREDOS Business
        Case [19]) and a reduced environmental impact (see CREDOS Environmental Case [20]).
        Emphasis is to be put on the fact that CREDOS is not expected to add strategic capacity in
        terms of scheduled slots. However, during stable weather conditions, CREDOS can also be
        used for short term tactical planning purposes by forecasting the supposed length of the period
        when CREDOS would most likely be operated.

        The actual benefits are dependent on traffic composition, the usage of the runway and the SID
        structure. So far only the case of a single independent runway used for departures has been


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        explored, but there is reason to believe that there would also be benefits in more complex
        situations.

        During the Euroben project, a runway simulation tool was used to model the potential benefits
        that could be obtained if reduced departure separations were employed under a suitable level of
        crosswind. Several European airports were investigated and a detailed study was carried out on
        London Heathrow (see [3] for further details).

        It is also worth noting that crosswind concepts for arrivals aimed at short/midterm
        implementation has yet to be defined.




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5. CONCLUSIONS AND FUTURE OPTIONS
        It is commonly acknowledged that, in today’s operations, the application of wake turbulence
        separation minima constitutes one of the constraints that limits airport capacity.

        Among other potential solutions, the CREDOS project is investigating the possibilities of safe
        conditional reduction of separation minima for departure, by suspending the wake turbulence
        separation minima under specific crosswind conditions, resulting in improved runway
        throughput.

        The basic idea behind CREDOS is that, for departures, the wake turbulence separation criteria
        may be relaxed on the runway and for the first part of the climb path when the crosswind is such
        that the wake turbulence generated by the preceding aircraft will have been blown out of the
        departure track of the succeeding aircraft (see section 3.2).

        The benefits of the proposed concept would be a temporary increase of the departure runway
        throughput in such a way that it absorbs capacity peaks or reduces departure delays. This
        increase occurs only when an aircraft of lighter wake category directly follows a heavier one and
        the CREDOS criteria are met. Only in such cases is there a potential for reducing the spacing
        between that aircraft pair compared to the wake turbulence separation that would otherwise
        have to be applied. The actual benefits would then also be dependent on traffic composition,
        usage of the runway and the SID structure (see section 3.2.4).

        So far, the concept focuses only on the suspension of the 2-minute (5/6 NM) start interval
        applicable for HEAVY – MEDIUM, HEAVY – LIGHT or MEDIUM – LIGHT aircraft combinations.
        It is based on today’s technical environment and does not require advanced tools such as
        DMAN or electronic flight strips.

        Nevertheless, the safe application of CREDOS separation suspension would require new
        information to be considered by controllers. It is therefore recommended that dedicated HMI
        and support tools be developed (see section 3.3.4).

        CREDOS is a wind-dependent concept. Consequently, the safe application of the concept
        requires the wind conditions to be monitored in the area surrounding the aircraft departure path.
        The range of the concept applicability is thus dependent on the wind monitoring capabilities of
        the airport (wind measurements, wind nowcast and/or forecast). The monitoring capabilities
        limitation leads to the definition of a volume surrounding the aircraft departure path within which
        the wind can be monitored and within which the wake turbulence separation may be suspended
        (the ‘Wake Turbulence Separations Suspension Airspace Volume’ (WTSSAV)). Indirectly, it also
        implies that the definition of CREDOS spacing (either expressed as a time interval or a distance
        one or both) will satisfy all CREDOS requirements (see section 3.2.2). It is for those in charge of
        local implementation to determine the underlying algorithms that define the CREDOS wind
        level.

        From the controllers’ point of view, the only major change in the roles and procedures of
        controllers introduced by the CREDOS concept is that when it is applied, it is presumed that it is
        the runway controller who is responsible for ensuring aircraft separation after departure,
        including the monitoring of the transition from CREDOS-reduced separation to the ICAO
        standard wake turbulence distance separations (see section 3.3.1).

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        Future options

        At this stage, the CREDOS concept has been kept as generic and as simple as possible. This
        document is thus to be considered rather as guidance material than as a description of one
        particular endorsed solution.

        A number of improvements are also envisaged for the future.

        For instance, an enhanced HMI able to take into account the wake turbulence categories of
        aircraft and their respective SID, in addition to the crosswind criteria, integrated into the GO/NO-
        GO indicator could ease the task of controllers.

        In the same way, the use of electronic flight strips would also ease the controller tasks and
        therefore reduce workload.

        The use of a modified DMAN that is able to account for CREDOS suspension of separation
        minima would be beneficial for the more tactical planning of runway capacity.

        By exploiting A-SMGCS, an automatic detection of aircraft take-off roll could be linked to the
        spacing between departures.

        By using flight plan data and even more detailed aircraft data (down-linked) such as current
        take-off weight and expected climb profiles, the trajectories of each departure could be
        calculated and fed into the controller HMI tools such as the trigger advisory line. This would
        allow for shorter distances between departures and dynamic spacing, pair by pair, as buffers
        could be decreased when accuracy for each aircraft involved increases.

        The deployment of enhanced weather-monitoring equipment with extended capabilities, such as
        LIDAR, would allow the WTSSAV to be extended and therefore to increase the benefits of
        CREDOS. Real-time down-linking of wind conditions from departing aircraft may be considered
        as another solution for enlarging the WTSSAV.

        Wider look-ahead accurate weather forecasts would also increase the benefits of CREDOS and
        would make the use of CREDOS more predictable.

        So far, super HEAVY aircraft and intersection departures have been disregarded in the concept
        development. Incorporating them into the concept could be considered as an option for future
        development of CREDOS.

        The concept is focussing on the suspension of wake turbulence minima on a single runway
        used in segregated mode for departure. The extension of the concept to mix-mode and for
        arrivals is also of major interest for improving the efficiency of airport operations in the future.




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6. CONCEPT EVOLUTION
        Scope has changed over the versions. Safety, Benefit, Environmental and HF Cases has used
        different versions during the project lifecycle. Results and advice from other WP’s as well as the
        Human factors activities were the main input for Concept development.


6.1. TIMELINE
                  Initial concept drafting                                                      2006

                  Conops version A                                        Spring                2007

                  Human Factors Issue Analysis                            May                   2007

                  HMI prototyping                                         Summer                2007

                  Task analysis                                           Sep                   2007

                  Stakeholder workshop                                    Nov                   2007

                  Cognitive task analysis                                 Feb                   2008

                  Conops version B                                        March                 2008

                  Field study 9 airports                                  Jul                   2008

                  Conops version C                                        Oct                   2008

                  RTS1                                                    Nov                   2008

                  RTS2                                                    Apr                   2009

                  Conops version D                                        Apr                   2009

                  Conops version E                                        Nov                   2009


6.2. CHANGES IN VERSION B COMPARED TO A
                  References listed in paragraph 1.4 excluded

                  All annexes deleted

                  Technical information about the CREDOS project as such is to a large part deleted.

                  LIGHT weight category included

                  A 380 excluded

                  Intersections excluded

                  Up to 3000 ft or 4 Nm is excluded as the limitation of CREDOS applicability.

                  CREDOS objectives paragraph excluded

                  Approach supervisor added in role description

                  In general less emphasis on CFMU descriptions


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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION


                  Delegation of control to tower during first climb phase as a requirement has been
                   excluded or less clearly expressed

                  Ground Controller description slightly changed.

                  Runway Controller description includes text about support tools and a clause about the
                   variability in rules and procedures over different airports is included.

                  To record whenever a CREDOS departure has been allowed, is added.

                  Further text added to explain figure 2.

                  Paragraph 3.2.1.7 describing all actors in a table format has been adjusted.

                  Cross wind component display for all runways excluded as requirement

                  Chapter 5 about the iterative process excluded

                  Conclusions and future options rewritten listing major changes compared to today’s
                   operations and also listing future options such as:

                        o     Supplementary geographically parallel SID’s can be introduced at an airport to
                              be used by MEDIUM and LIGHT aircraft when upwind crosswind conditions are
                              in place. Environmental, traffic management and infrastructural constraints
                              have a big impact on the outcome of such an investigation.

                        o     Improvement of the departure sequence management by using DMAN.

                        o     The integration of SUPER HEAVY aircraft

                        o     Suspension of the 3 minute rule when using intersection

                        o     Real time down linking of wind conditions from departing aircraft feed the
                              system to enhance the applicability of the concept.

                        o     The integration in DMAN

                        o     Forecast accuracy such that a wider look-ahead window can be determined
                              and a new departure rate can be widely communicated.


6.3. CHANGES IN VERSION C COMPARED TO B
                  Field studies led to the conclusion that HMI development and procedures is highly
                   dependant on local environment and constraints

                  References are added.

                  Text added in the scope:

                        o     Other criteria than the crosswind component needed

                        o     Case by case has been replaced by “by aircraft pair”

                        o     New sentence about radar environment and responsibilities

                  New terminology added

                  Criteria for applying the wake turbulence rules has been corrected

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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION


                  In Chapter 3 figures has been changed and added

                  Applicability of the concept now changed to: typically up to 1500 ft

                  Text describing the transition to wake turbulence radar separation after the first climb
                   phase is introduced

                  Decision tree and determination of how the CREDOS spacing is determined has been
                   added

                  Clearance Delivery added as the role who informs flight crew about CREDOS being in
                   use.

                  Actors table improved in detail

                  No annexes as this version was used mainly as preparation for RTS1


6.4. CHANGES IN VERSION D COMPARED TO C
                  Main changes are due to RTS1 findings and the preparations needed for RTS2

                  By the participation of controllers from many different airports it is further verified that
                   one solution for procedures and HMI will never fit all

                  More illustrations added

                  Annexes attached

                  The separation mode for a given airport is describes as either time or distance or a
                   combination of both depending on selected HMI


6.5. CHANGES IN VERSION E COMPARED TO D
                  All final review comments from the partners were considered

                  Professional proof reading was conducted

                  Peer review was conducted

                  Executive Summary was changed and extended

                  Text was reorganised

                  HMI and concept was described more high level and generic

                  HMI illustrations has been changed and/or added

                  Examples of specific HMI solutions from RTS2 was added as annex

                  The determination of the separation for a given airport is described in annex A

                  A concept evolution chapter has been added




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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION



7. REFERENCES
        CREDOS external references

     1. EUROCONTROL (SRC Document 12), Assessment of the EATMP ‘Air Navigation System Safety
          Assessment Methodology’ as means of compliance with ESARR4.

     2. EUROCONTROL (SRC Document 33), Assessment of the ‘LVNL safety criteria’ as a means of
          compliance with ESARR4, August 2004.

     3. EUROCONTROL Performance Review Commission, Performance Review Report (PRR7), April
          2004.

     4. EUROCONTROL Safety R&D Seminar, LVNL Safety criteria, 21 September 2007.

     5. EUROCONTROL, Study on Constraints to Growth, March 2001.

     6. European Wake Vortex Mitigation Benefits Study – EUROBEN (ISDEFE & NATS), WP3 Deliverable,
          High Level Benefits Analysis & Systemic Analysis, November 2005.

     7. FAA/NASA WakeVAS ConOps Evaluation Team, Crosswind-Dependent Arrivals Mid-Term
          Candidate Operational Enhancement Phase II-B, July 11th, 2005.

     8. FAA/NASA WakeVAS Conops Evaluation Team, Crosswind-Dependent Departures Mid-Term
          Candidate Operational Enhancement Phase II-A, July 11th, 2005.

     9. ICAO Doc 4444 ATM/501, Procedures for Air Navigation Services - Air Traffic Management, 15th
          edition, 2007.

     10. SAM Electronic, European Air Traffic Management EATMP, SAM V 2.1, 2006.


        CREDOS internal references

     11. CREDOS – Annex I, Description of Work, Version 2, October 2006.

     12. CREDOS Deliverable D2-1, EDDF-1 Data Collection Campaign Report, February 2008.

     13. CREDOS Deliverable D2-4, EDDF-2 Data Collection Campaign Report, May 2008.

     14. CREDOS Deliverable D2-5, EDDF-2 database analysis & performance assessment of the Wake
          Vortex Models on the EDDF-1 and EDDF-2 databases, 2009.

     15. CREDOS Deliverable D4-1, Operational & System Requirements.

     16. CREDOS Deliverable D4-2, Initial Concept, 2007.

     17. CREDOS Deliverable D4-4, Plan for ESARR Conformance, Version 01, 2007.

     18. CREDOS Deliverable D4-10, Human Factor Case Report, July 2009.


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     19. CREDOS Deliverable D4-13, Business Case.

     20. CREDOS Deliverable D4-14, Environmental Case.

     21. CREDOS Deliverable D4-15, Real-time Simulation Conduct Report, May 2009.

     22. CREDOS Technical Note (J. MORVAN, E. ISAMBERT), Current Practices For Departure
          Operations, 2001.




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8. LIST OF FIGURES
Figure 1: Illustration of the CREDOS WTSSAV determined by the wind monitoring capabilities of
     the airport. Inside the WTSSAV, when CREDOS may be applied, the wake turbulence
     separation minima may be suspended. Outside, the standard ICAO wake turbulence minima
     apply. ....................................................................................................................................... 17 
Figure 2: Decision-making process for determining the suitable CREDOS reduced spacing......... 20 
Figure 3: SID consideration scheme. In this case, if the second aircraft is on the same SID as the
     leader (i.e. SID3), CREDOS is allowed. If the second is on any other SID (both downwind)
     CREDOS is not allowed. Note that there are no upwind SIDs in the example. ....................... 21 
Figure 4: Nominal departure flight decision flow (without CREDOS). ............................................. 24 
Figure 5: Scheme of the hierarchy of the different CREDOS statuses. .......................................... 33 
Figure 6: Example of a CREDOS HMI when CREDOS is ‘not available’........................................ 35 
Figure 7: Example of a CREDOS tower supervisor HMI when CREDOS is ‘not active’. ................ 36 
Figure 8: Example of a CREDOS HMI when CREDOS is ‘not active’ (all working positions)......... 36 
Figure 9: Example of a CREDOS HMI when CREDOS is ‘active’ and the CREDOS wind level is
     met........................................................................................................................................... 36 
Figure 10: Example of a CREDOS HMI when CREDOS is ‘active’ and the CREDOS wind level is
     not met..................................................................................................................................... 36 
Figure 11: Example of a support tool developed to aid controllers to determine whether or not SID
     geometry permits the suspension of the wake turbulence separation in case of GO (from
     CREDOS real-time simulations – session 2). .......................................................................... 37 



     Annexes
Figure 12: Distribution of y at x=4,000 m (x=0 is the start of the runway) in the measured aircraft
     population (see [13]). ............................................................................................................... 54 
Figure 13: Distribution of y at x=6,000 m (x=0 is the start of the runway) in the measured aircraft
     population (see [13]). ............................................................................................................... 55 
Figure 14: Decision-making process to determine the suitable CREDOS reduced spacing........... 57 
Figure 15: Evolution of the vortex net lateral displacement as a function of the crosswind
     (v(h = 10 m)) at different times. At each time, a linear fit (black) shows the mean evolution.
     Envelopes containing 90% (green), 95% (cyan) and 99% (magenta) of the total examined
     vortices are also drawn............................................................................................................ 58 
Figure 16: Aircraft radar separation at follower rotation time (CREDOS time spacing of 60
     seconds). Each star represents one of the 44 possible aircraft pairs that can be built on the
     basis of the traffic mix considered. The red line highlights the minimum radar separation value.
     ................................................................................................................................................. 59 
Figure 17: Aircraft radar separation when the follower comes out of the WTSSAV (CREDOS time
     spacing of 60 seconds). Each star represents one of the 44 possible aircraft pairs that can be
     built on the basis of the traffic mix considered. The red line highlights the ICAO wake
     turbulence separation minimum for HEAVY-MEDIUM. ........................................................... 60 
Figure 18: Idem (CREDOS time spacing of 85 seconds). .............................................................. 60 
Figure 19: Aircraft radar separation at follower rotation time (CREDOS distance spacing of 2.0
     NM). Each star represents one of the 44 possible aircraft pairs that can be built on the basis of
     the traffic mix considered. The red line highlights the minimum radar separation value. ........ 62 
Figure 20: Aircraft radar separation when the follower comes out of the WTSSAV (CREDOS
     distance spacing of 2.0 NM). Each star represents one of the 44 possible aircraft pairs that
     can be built on the basis of the traffic mix considered. The red line highlights the ICAO wake
     turbulence separation minimum for HEAVY-MEDIUM. ........................................................... 63 
Figure 21: Idem (CREDOS distance spacing of 2.9 NM)................................................................ 63 
Figure 22: Radar display with the Take-off Trigger Advisory Line (orange line) used for the real-
     time simulations. The 3 SIDs considered during the simulations are highlighted by the dashed
     green lines. .............................................................................................................................. 64 
9. LIST OF TABLES
Table 1: Current wake turbulence separation minima for departures. ............................................ 11 
Table 2: Actors and changes to the role when using the CREDOS concept .................................. 31 
Annexes
                                FINAL CONCEPT OF OPERATIONS DESCRIPTION



A. EXAMPLE OF CREDOS IMPLEMENTATION (USED
  FOR CREDOS REAL-TIME SIMULATIONS)
        This section describes how the CREDOS concept has been implemented for the
        evaluation/validation real-time simulation task performed in work package 4.3 (see [21] for
        further details on the real-time simulations).

        First of all, it is important to note that the real-time simulations (RTS-2, see [21]) have been
        developed on the basis of version D of the CREDOS concept. The major modification from
        version D to version E is that the latter is somewhat more generic and leaves rooms for
        adjusting the concept to local constraints and environment.

        The changes between the two versions of the concept, and how these changes impact the
        implementation, are depicted in the first part of this section. There follows a step-by-step
        description of how the CREDOS spacing has been determined for the real-time simulations.
        Finally, the HMI solutions developed for the simulations are illustrated.

        In each section, the impact of the concept modification, if any, is described.

        It should also be noted that for the RTS implementation of CREDOS concept, data from
        different sources collected at different places in the different work packages of CREDOS project
        have been used together. For instance, the airport layout is close to the Schipol layout but the
        wind data and the wake turbulence transport data come from Frankfurt airport.

        Of course, in case of local implementation, all data used have to be collected locally.

        It is important to note that any numbers or values used in this example are not fully validated or
        correlated and must therefore not be considered as indicative for a local implementation case.


A.1. CHANGES BETEWEEN CREDOS CONCEPT VERSION D AND
   VERSION E
        As mentioned above, the main modification from the CREDOS concept version D and this final
        version (version E) is that some parts of the latter have been made more generic and therefore
        easier to adapt to local constraints and environment.

        For instance, in version D of the concept, the CREDOS spacing is assumed to be a distance
        spacing. But it is known that many airports in Europe apply a time spacing between consecutive
        departures, and some of them would be reluctant to switch from time spacing in ‘normal’
        operations to distance spacing when CREDOS suspension of the wake turbulence minima
        apply, and then back to the time spacing when the wake turbulence separation may no longer
        be suspended.

        Therefore, this latest version of the concept describes how to determine the CREDOS spacing
        (regardless of whether it is a time-based or a distance-based spacing) rather than focussing on
        the description of one particular solution.

        The same reasoning can be made for the HMI. The CREDOS HMI has to be integrated into a
        local tower environment that might significantly differ from one place to another. Hence, rather
        than describing one single HMI solution suitable for CREDOS, the HMI functionalities and the
        information required to be able to apply CREDOS operations are described.

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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION


A.2. DETERMINATION OF THE WTSSAV SIZE
        CREDOS spacing depends on the local WTSSAV size. Hence, the first element to determine is
        the size of the Wake Turbulence Separations Suspension Airspace Volume. This section
        describes how this was done for the real-time simulation exercises. It is a detailed description of
        the process presented in section 3.2.2.

        The size of the WTSSAV always has to be defined locally on the basis of local wind monitoring
        means (height of the airspace volume), the locally determined crosswind component threshold,
        in conjunction with aircraft capability to accurately navigate their departure paths (width of the
        airspace volume) and the actual layout and construction of the SIDs.

        Height of the WTSSAV

        The height of the WTSSAV is determined by the vertical range limitation of the airport wind-
        monitoring equipment. For the real-time simulations, it has been assumed that wind can be
        monitored with a sufficient accuracy for CREDOS operations up to 2,000 ft.

        Width of the WTSSAV

        The lateral size of the WTSSAV is determined by the required width of the wake turbulence
        safety corridor around the path of the departing aircraft. The width of the corridor is established
        on the basis of safety arguments taking into account the range of the wind assessment
        equipment (which should not constitute a limitation) and the capability of the aircraft to
        accurately navigate their departure paths.

        During the EDDF-2 data collection campaign, aircraft trajectories were measured, and the
        lateral deviation of aircraft from their track computed. Figure 12 and Figure 13 from [13] show
        the distribution of the aircraft lateral deviation for HEAVY and MEDIUM aircraft at 4,000 m and
        6,000 m from the start of the runway respectively. It can be observed that a 300 m-wide corridor
        is enough to maintain the probability of having aircraft navigating out of the expected route at an
        acceptably low level.




    Figure 12: Distribution of y at x=4,000 m (x=0 is the start of the runway) in the measured aircraft
                                           population (see [13]).

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    Figure 13: Distribution of y at x=6,000 m (x=0 is the start of the runway) in the measured aircraft
                                           population (see [13]).


        To summarize, the WTSSAV used for the real-time simulation size then becomes:

                  2,000 ft height;

                  300 m width (150 m to either side of the runway centreline).

        The length of the airspace volume is computed on the basis of the aircraft climb rate
        performance. For the traffic mix used in the real-time simulation, and using the simulator aircraft
        performance model, the length of the WTSSAV is approximately 6,000 m (3.2 NM).

        It is to be noted that the length of the airspace volume has no significant impact on the
        CREDOS concept (no impact on the CREDOS spacing).

        The modification of the concept from version D to version E has no impact on the determination
        of the WTSSAV size.




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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION



A.3. DETERMINATION OF CREDOS SPACING
        Once the Wake Turbulence Separations Suspension Airspace Volume has been sized, the
        suitable CREDOS spacing has to be determined. This section describes how to evaluate this
        spacing. It illustrates the process developed in section 3.2.3.

        As mentioned earlier, the suitable spacing may be either a time or a distance spacing (or both),
        and it is a local responsibility to select the more appropriate.

        In version D of the concept, and therefore for the real-time simulations, only distance spacing
        was applied.

        In this section the iterative process will be described twice in order to determine first the suitable
        distance spacing (as done for the real-time simulation) and then to find a suitable time spacing
        for the application of CREDOS operations.

        It is stated in section 3.2.3 that the CREDOS spacing has to satisfy all of the following three
        conditions:

             1. the time elapsed between two departures, when CREDOS wake turbulence separation
                minima are suspended, has to be sufficient to ensure that the wake turbulence is
                transported out of the departure path;

             2. consecutive departing aircraft always have to be separated by at least the applicable
                ATS surveillance system based separation minimum (usually 3.0 NM);

             3. transition from CREDOS spacing to ICAO standard wake turbulence separation has to
                be made prior to the point at which the succeeding aircraft reaches the upper boundary
                of the WTSSAV.

        It is also stated that this can be ensured by the use of a general iterative decision-making
        process illustrated by the decision tree in Figure 14.

        Before entering into the details of the process, a number of remarks need to be made.

        Firstly, it is worth noting that the process applies whatever the spacing means - there is no
        difference between distance-based and time-based spacing.

        Secondly, it should be noted that all constraining parameters depend on the aircraft
        performances and therefore the traffic mix considered, and on the pre-determined crosswind
        threshold. The latter has to be determined by a local assessment of wind conditions and is the
        result of a compromise. On the one hand, one would like to have a value for the crosswind
        component threshold as high as possible so that the time required to transport the wake
        turbulence out of the departure path is short, but on the other hand, one would also like the
        threshold to be as low as possible in order to be able to benefit more often from CREDOS. The
        first results of CREDOS work package 2 (see [12]), indicate that a crosswind component of
        about 7 kts for a separation of about 90 seconds is a reasonable assumption for the minimum
        crosswind threshold limit needed for safe CREDOS application. It has thus been assumed for
        the real-time simulations, that a threshold of 7 kts (3.6 m/s) would be a suitable compromise.




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        Finally, it is important to note that a buffer time of 15 seconds has been built in for the controller
        to read the take-off clearance and the pilot to then actually start the aircraft roll. This buffer,
        called the ‘reaction time’ has been taken into account for the computation of aircraft spacing.



        For the real-time simulations, the traffic mix was initially made up of the following aircraft types:

                  4 HEAVY: A306, A333, B744, and B763;

                  11 MEDIUM: A319, A320, A321, B733, B735, B738, CRJ2, E145, F100, F50, and
                   MD83.

        The total number of possible HEAVY-MEDIUM aircraft pairs from this traffic mix is thus 44.

        The suitable CREDOS spacing was computed on the basis of this traffic mix using the tower
        simulator’s aircraft performance model (see [21] for further details). At a later point in time one
        LIGHT aircraft type was added to the mix sample: C550 but the spacing was not modified.




        Figure 14: Decision-making process to determine the suitable CREDOS reduced spacing.




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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION


        Time Spacing

        Assuming that the CREDOS spacing determination process is based on time, and starts from
        the initial value of 60 seconds, which is the minimum runway time separation between two
        consecutive departures when the aircraft pair does not require any wake turbulence separation
        (e.g. MEDIUM-MEDIUM, MEDIUM-HEAVY, ...).

        The first step is to determine whether the wake turbulence is outside the path of the follower
        aircraft when airborne. On the basis of work package 2 results, it can be shown that for a
        surface crosswind component of 7 kts (measured at 10m height), the wake vortices generated
        by the leading aircraft are transported a distance greater than 150m in a timeframe of 80
        seconds. Figure 15 (from [14]) presents the lateral displacement of the wake vortices as a
        function of the surface crosswind at different times. In the 80 seconds subplot, the vertical red
        line stands for the 7 kts (3.6 m/s) crosswind component. The mean displacement (black line) is
        approximately 320 m, and the minimum displacement of the 95% envelope (delimited by the
        cyan lines) is 166 m. In other words, the statistical analysis of the data collected during the
        CREDOS project shows that, for a surface crosswind component of 7 kts after 80 seconds, less
        than 2.5% of the wake vortices have not been transported a distance of 166m.

        Consequently, 80 seconds is assumed to be sufficient to transport the wake turbulence out of
        the track of the following aircraft for a corridor of half 300 m width (equal to 2 x 150 m).




      Figure 15: Evolution of the vortex net lateral displacement as a function of the crosswind
(v(h = 10 m)) at different times. At each time, a linear fit (black) shows the mean evolution. Envelopes
containing 90% (green), 95% (cyan) and 99% (magenta) of the total examined vortices are also drawn.

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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION


        Based on the performance model of the simulator, for the aircraft considered in the traffic mix,
        the shortest time period elapsed between the clearance of the first aircraft and the rotation of
        the second one when applying 60 seconds between roll of number one to clearance delivery of
        the succeeding (overall 44 possible aircraft pairs in the mix) is 86 seconds (for aircraft pairs with
        A319 or F50 as follower). The first constraint is thus satisfied.

        The second step is to ensure that the minimum radar separation (3.0 NM) is obtained when the
        second aircraft becomes airborne. Figure 16 shows the aircraft radar separation at the follower
        aircraft rotation time. For each of the 4 HEAVY aircraft (abscise axis), the radar separation at
        rotation time of all of the 11 MEDIUM aircraft (11 stars of same colour) has been computed. It is
        seen in the figure that all aircraft pairs reach separation higher than the required 3.0 NM. This
        means that a time spacing of 60 seconds is sufficient to satisfy the second constraint.




 Figure 16: Aircraft radar separation at follower rotation time (CREDOS time spacing of 60 seconds).
 Each star represents one of the 44 possible aircraft pairs that can be built on the basis of the traffic
             mix considered. The red line highlights the minimum radar separation value.

        The third step is to ensure that the ICAO standard wake turbulence separation minima are
        obtained when the second aircraft comes out of the WTSSAV. Figure 17 shows the aircraft
        radar separation at the time when the follower aircraft reaches the airspace volume vertical limit
        (i.e. 2,000 ft for RTS-2). It can be observed that most of the possible aircraft pairs do not obtain
        the ICAO required 5.0 NM. The 60 seconds time spacing is thus too short and has consequently
        to be gradually increased until all aircraft pairs obtain separation higher than or equal to 5.0 NM.

        Step by step, the time spacing is increased, and the computation of the aircraft radar separation
        is performed until the third constraint is satisfied.

        It is seen in Figure 18 that, 85 seconds is the minimum time spacing required to ensure that all
        aircraft pairs reach at least a radar separation of 5.0 NM.

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   Figure 17: Aircraft radar separation when the follower comes out of the WTSSAV (CREDOS time
spacing of 60 seconds). Each star represents one of the 44 possible aircraft pairs that can be built on
 the basis of the traffic mix considered. The red line highlights the ICAO wake turbulence separation
                                     minimum for HEAVY-MEDIUM.




                                Figure 18: Idem (CREDOS time spacing of 85 seconds).


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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION


        Conclusively it was determined that, for the WTSSAV and the traffic mix (and aircraft
        performance model) of the real-time simulations, the minimum suitable time spacing for
        CREDOS should be 85 seconds.




        Distance Spacing (solution implemented for the real-time simulations)

        For CREDOS spacing based on distance, the process can be initiated, for instance, from a
        value of 2.0 NM, which is approximately the length of the runway used for the real-time
        simulations. This means that the second aircraft will not be cleared for take-off until the first
        covers a distance of 2.0 NM from the start of the runway.



        The first step is, again, to determine whether the wake turbulence is outside the path of the
        follower aircraft when airborne. It was shown above that 80 seconds is enough for a surface
        crosswind component of 7 kts to transport 97.5% of the wake vortices a distance of at least
        150 m.

        Based on the performance model of the simulator for the aircraft considered in the traffic mix, in
        the case of a CREDOS spacing of 2.0 NM, the shortest time period elapsed between the
        clearance of the first aircraft and the rotation of the second one (over all 44 possible aircraft
        pairs in the mix) is 85 seconds (for B744-A319 and B744-F50 aircraft pairs).

        The first constraint is thus satisfied.



        The second step is, again, to ensure that the minimum radar separation (3.0 NM) is obtained
        when the second aircraft becomes airborne. Figure 19 shows the aircraft radar separation at the
        follower aircraft rotation time. For each of the 4 HEAVY aircraft (abscise axis), the radar
        separation was computed at rotation time of all of the 11 MEDIUM aircraft (11 stars of same
        colour). It is seen in the figure that all of the aircraft pairs obtain separation higher than the
        required 3.0 NM.

        Therefore, the 2.0 NM distance spacing also satisfies the second constraint.




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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION




 Figure 19: Aircraft radar separation at follower rotation time (CREDOS distance spacing of 2.0 NM).
 Each star represents one of the 44 possible aircraft pairs that can be built on the basis of the traffic
            mix considered. The red line highlights the minimum radar separation value.




        The third step is, again, to ensure that the ICAO standard wake turbulence separation minima
        are obtained when the second aircraft comes out of the WTSSAV. Figure 20 shows the aircraft
        radar separation at the time the follower aircraft reaches the airspace volume vertical. It can be
        observed that most of the possible aircraft pairs do not obtain the ICAO required 5.0 NM. The
        2.0 NM distance spacing has thus to be gradually increased until all aircraft pairs obtain
        separation higher than or equal to 5.0 NM.

        It can be seen in Figure 21 that 2.9 NM is the minimum distance spacing required to ensure that
        all aircraft pairs reach at least a radar separation of 5.0 NM.

        It can therefore be conclusively determined that, for the WTSSAV and the traffic mix (and
        aircraft performance model) of the real-time simulations, the minimum suitable distance spacing
        for CREDOS is 2.9 NM. This is therefore the value used for the real-time simulations.




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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION




Figure 20: Aircraft radar separation when the follower comes out of the WTSSAV (CREDOS distance
spacing of 2.0 NM). Each star represents one of the 44 possible aircraft pairs that can be built on the
  basis of the traffic mix considered. The red line highlights the ICAO wake turbulence separation
                                    minimum for HEAVY-MEDIUM.




                                 Figure 21: Idem (CREDOS distance spacing of 2.9 NM).


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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION



A.4. HMI AND SUPPORT TOOLS
        All HMI and support tools developed for the real-time simulations are described in [21].

        This section only presents the runway controller HMI developed for the CREDOS real-time
        simulations, which helps to determine the spacing between two departures. As already stated,
        the real-time simulations were based on version D of the CREDOS concept (which focussed
        only on a distance-based spacing for CREDOS operations).

        To help the runway controller to determine when the suitable CREDOS distance spacing has
        been covered by the leader aircraft, and thus when the clearance can be read to the follower, a
        mark on the radar display was added that represents the CREDOS spacing. This orange circle
        arc line, see Figure 22, only appears on the display when CREDOS status is GO (i.e. when
        CREDOS system is available, is active and the wind conditions are such that CREDOS
        suspension of wake turbulence separation may be applied. The dashed green lines represent
        the 3 SIDs considered during the real-time simulations.




 Figure 22: Radar display with the Take-off Trigger Advisory Line (orange line) used for the real-time
simulations. The 3 SIDs considered during the simulations are highlighted by the dashed green lines.




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B. USE CASES
        The purpose of the use cases developed for the CREDOS concept is to specify the support
        provided by the automated system to the actors in the context of dynamic situations (scenarios
        – alternatives – failures). The use cases are utilised during the validation and refinement of the
        concept for:

             -     Development of a system architecture

             -     Safety case development

             -     Communication activities about the concept

        The CREDOS Use Cases are based on the simplest foreseen type of operational HMI support
        needed to apply the reduction in departure separation, its main features being as follows:

             -     A timer HMI function is available for RWY controller.

             -     CREDOS system status can be monitored from the tower supervisor position. Only in
                   the tower supervisor position can the system be activated. CREDOS activated/non
                   active indicator is available for tower supervisor, tower runway controller and TMA
                   departure controller. In tower supervisor, runway and TMA departure positions it can be
                   deactivated independently.

             -     CREDOS crosswind indicator available for RWY controller and tower supervisor.

             -     CREDOS available/not available indicator available for tower runway controller.

             -     Windsock at the beginning of the runway is available for flight crews.

             -     There is no automatic detection of commence of take-off roll.

             -     There is no DMAN.

             -     CREDOS functionality is not integrated into electronic flight strips.

        The system is able to determine when the CREDOS wind criteria are met per runway. Those
        criteria are not yet determined but are based on existing wind measurements per runway,
        including crosswind, gust strength and direction and some nowcasting logic.

B.1. ACTIVATE CROSS-WIND DEPARTURES

        Summary

        This Use Case describes how the tower supervisor uses the system to verify that the criteria to
        apply the CREDOS departure procedure are met and how CREDOS operations are activated
        and de-activated.


        Actors' roles

        Tower supervisor (primary) – wants to make sure that CREDOS is correctly activated and used
        in a safe and efficient manner.



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        Tower runway controller (support) – wants to make sure that the aircraft takes off in a safe
        manner with respect to the risk of collision with other traffic or obstacles and to maintain safe
        separation with other aircraft and wants to optimise the sequence and the efficiency of the
        departure flow and the departure rate.

        ACC supervisor (support) – wants to be informed of CREDOS being in use.

        ACC flow manager (support) – wants to know when CREDOS is used or foreseen to be used.

        Tower clearance delivery (support) – wants to inform flight crews that CREDOS is being
        applied.

        Tower ground controller (off-stage) – wants to be informed of changes in the departure rate
        which will affect the departure sequence.

        Flight crew (off-stage) – has to ensure that the aircraft takes off safely and efficiently.

        TMA departure controller (off-stage) – has to take control of the aircraft from the tower runway
        controller after the take-off. Wants to know when CREDOS is active/non active.


        Pre-conditions

        CREDOS operations are not activated. MET reports indicate that winds will be strong enough
        for applying CREDOS. Planning of runway configuration is ongoing.


        Post-conditions

        Successful end state

        The system has correctly indicated technical status and CREDOS availability/non availability.

        Failed end state

        One or more components of the CREDOS system out of service and CREDOS procedure
        cannot be activated. The benefit of crosswind departures cannot be realised. Foreseen delays
        cannot be mitigated.


        Trigger

        The Use Case starts when the tactical choice of runway configuration is about to be completed.


        Main flow - activating crosswind operations

             1. Tower supervisor checks all input needed in order to apply the safest and efficient
                runway configuration for the next appropriate time period. This input consists of traffic
                demand, traffic mix, traffic balance load (arrivals vs departures), critical weather data,
                runway management policies (noise abatement), work in progress, runway and arrival
                instrument technical status etc.

             2. Tower supervisor uses the system in order to evaluate the possibility of choosing
                runways in such a way that the benefit of crosswind operations can be realised.

             3. The system indicates that all sensors and services are correct.


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             4. The system indicates that the crosswind criteria are met.

             5. Tower supervisor chooses runway configuration. At least one runway will be used for
                crosswind departure operations.

             6. Tower supervisor informs ACC supervisor about runway configuration and expected
                runway throughput.

             7. Tower supervisor informs ACC flow manager about expected throughput (may also be
                done by ACC supervisor).

             8. Tower supervisor informs all concerned staff in the tower and activates CREDOS.

             9. Tower supervisor checks that “CREDOS operations” is added in the ATIS transmission.

             10. Tower supervisor checks that CREDOS go/no-go HMI in runway controller working
                 position is correctly displayed.

             11. Tower supervisor ensures that TMA departure controller is aware of CREDOS
                 operations being activated.

             12. The use case ends when the first aircraft pair subject to CREDOS has departed.


        Main flow - deactivating crosswind operations

             13. The system submits an alert showing that CREDOS conditions no longer are met or
                 that one or more System components are unserviceable.

             14. The system automatically shuts down the CREDOS Go indicator in tower runway
                 controller position and CREDOS available indicator in tower supervisor and TMA
                 departure controller positions.

             15. Tower supervisor informs ACC supervisor (and ACC flow manager) that CREDOS is no
                 longer active.

             16. Tower supervisor ensures that all concerned staff in the tower are aware that CREDOS
                 operations are no longer in use.

             17. Tower supervisor checks that the ATIS information is changed.

             18. The use case ends when all concerned are informed about CREDOS being
                 deactivated.


        Alternative flow(s)

        Alternative to Step [13]: MET office, flight crew or controller reports unsuitable conditions for
        applying CREDOS.

             19. Tower supervisor deactivates the CREDOS system by using the HMI in the working
                 position consol.

             20. Resume main flow, step [15-18].


        Failure flow(s)


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        Any step – CREDOS System is unserviceable.

             21. Tower supervisor informs concerned staff in the tower that normal departure separation
                 remains applied.




B.2. HANDLE TAKE-OFF MOVEMENT IN CROSS-WIND CONDITIONS

        Summary

        This use case describes how a tower runway controller uses the system to verify that the aircraft
        takes off in a safe and efficient manner, while reducing delays because of beneficial crosswind.


        Actors' roles

        Tower runway controller (primary) – wants to make sure that the aircraft takes off in a safe
        manner with respect to the risk of collision with other traffic or obstacles and to maintain safe
        separation with other aircraft and wants to optimise the sequence and the efficiency of the
        departure flow and the departure rate. – needs to know what SIDs are upwind/downwind
        depending on the actual crosswind. – controls the first climb phase up to 2,500 ft before
        handing over to TMA departure control.

        Flight crew (support) – has to ensure that the aircraft takes off safely and efficiently.

        Tower ground controller (support) – wants to be informed of changes in the departure rate
        which will affect the departure sequence.

        Tower supervisor (support) – wants to make sure that CREDOS is correctly activated and used
        in a safe and efficient manner.

        TMA departure controller (support) – has to take control of the aircraft from the tower runway
        controller after the take-off - wants to know when CREDOS is active/non active.


        Pre-conditions

        The flight has completed the taxi out and is at the departure runway holding point. One or
        multiple runway line-up positions are in use.

        The transfer of responsibility between the tower ground controller and the tower runway
        controller is completed. Communication contact between the tower runway controller and the
        flight crew is established.

        CREDOS is active. Flight crew is informed about CREDOS being used and agrees to
        suspended separations being applied.

        Leader aircraft is HEAVY and follower aircraft is MEDIUM.


        Post-conditions

        Successful end state


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        The system has correctly proposed CREDOS as being available and the runway controller has
        correctly and safely applied it and where possible the runway rate has resulted in a higher
        number than the comparative ICAO WV rules would have resulted in.

        Failed end state

        Aircraft has not departed more efficiently than if ICAO WV had been applied.

        Aircraft has departed too close.


        Trigger

        The Use Case starts when the aircraft is at the runway holding point, ready to line up.


        Main flow

             1. The tower runway controller issues take-off clearance to a HEAVY leader aircraft.
                Tower runway controller uses the timer whenever needed behind HEAVY and MEDIUM
                aircraft in order to achieve the correct distance and time for the follower aircraft.

             2. Tower runway controller verifies that the aircraft pair are on suitable SIDs for CREDOS
                to be applied. Leading aircraft must be on same or downwind SID compared to the
                follower.

             3. Tower runway controller verifies that the leader aircraft has safely taken off and is
                following the assigned standard instrument departure (SID) procedure, the speed
                constraints and/or the minimum climb rate.

             4. The tower runway controller gives the clearance to the flight crew of the following
                aircraft for “line up and wait” via R/T.

             5. The flight crew lines up the aircraft.

             6. For follower aircraft: tower runway controller checks that CREDOS is still in available
                status and that CREDOS system indicates GO status, read the wind to the flight crew
                and gives the “ CREDOS “ take-off clearance to the flight crew via R/T.

             7. The flight crew releases the brakes, accelerates, rotates the aircraft and lifts-off.

             8. The tower runway controller verifies that the aircraft has safely taken off and is following
                the assigned standard instrument departure (SID) procedure, the speed constraints
                and/or the minimum climb rate.

             9. At the agreed point and/or altitude, the tower runway controller instructs the flight crew
                to transfer communications to the TMA departure controller.

             10. The use case ends when aircraft has contacted the TMA departure controller.


        Alternative flows

        CREDOS is activated while aircraft subject to CREDOS is lining up.

             11. Tower runway controller informs following aircraft that CREDOS is in use.

             12. Flight crew agrees to suspended separation.

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             13. The use case resumes at step 5.

        Alternative at step [3] or [4] flight crew unable to accept suspended WV clearance

             14. [3 or 4] The flight crew informs the tower runway controller that they want to apply ICAO
                 WV separation (or even additional spacing) instead of CREDOS.

             15. The tower runway controller will then not apply CREDOS suspension.

             16. Timer is used by the tower runway controller in order to achieve the correct ICAO WV
                 distance and time for the follower aircraft.

        Alternative at Step [2] or [7]. The first or second aircraft is deviating significantly from the
        departure procedure (SID route, speed constraint, minimum climb rate).

             17. Tower runway controller detects that the leading or following aircraft is deviating
                 significantly from the flight trajectory planned according to the departure procedure
                 (route, speed constraint, minimum climb rate).

             18. RWY notifies the flight crew and if necessary issues a WV warning message to the
                 following aircraft and a correction of track/SID to leading /follower.

             19. The tower runway controller contacts DEP and informs of corrective actions.

             20. Failure at Step [4]. The tower runway controller detects a take-off without clearance
                 being issued.

             21. Aircraft is taking off too close to preceding aircraft.

             22. Tower runway controller initiates avoiding action and traffic warning if necessary.

             23. Tower runway controller then ensures that the aircraft are correctly separated.

             24. Tower runway controller then issues a wake vortex encounter warning to the follower
                 aircraft if considered to be necessary.


        Failure flows

        Any step – CREDOS System is unserviceable.

             25. Tower runway controller de-activates the procedure for separation reduction.




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B.3. EXECUTE TAKE-OFF IN CROSS-WIND CONDITIONS

        Summary

        This Use Case describes how a flight crew takes off with a MEDIUM aircraft behind a HEAVY in
        a safe and efficient manner while being subject to suspended wake turbulence separation
        because of crosswind.


        Actors' roles

        Flight crew (primary) – has to ensure that the aircraft takes off safely and efficiently.

        Tower runway controller (support) – wants to make sure that the aircraft takes off in a safe
        manner with respect to the risk of collision with other traffic or obstacles and to maintain safe
        separation with other aircraft, – wants to optimise the sequence and the efficiency of the
        departure flow and the departure rate. – needs to know what SIDs are upwind/downwind
        depending on the actual crosswind. – controls the first climb phase up to 2,500 ft before
        handing over to TMA departure control.

        Executive TMA departure controller (support) – has to take control of the aircraft from the tower
        runway controller after the take-off. Wants to know when CREDOS is active/non active.

        Tower ground controller (offstage) – wants to be informed of changes in the departure rate
        which will affect the departure sequence.


        Pre-conditions

        The flight has completed the taxi out and is at the departure runway holding point. One or
        multiple runway line-up positions are in use.

        The transfer of responsibility between the tower ground controller and the tower runway
        controller is completed. Communication contact between the tower runway controller and the
        flight crew is established.

        CREDOS is active. Flight crew is informed about CREDOS being used and agrees to
        suspended separations being applied.

        Leader aircraft is HEAVY and follower aircraft is MEDIUM.


        Post-conditions

        Successful end state

        The system has correctly proposed CREDOS to be available and the runway controller has
        correctly and safely applied it and where possible the runway rate has resulted in a higher
        number than the comparative ICAO WV rules would have resulted in.

        Failed end state

        Aircraft has not departed more efficiently than if ICAO WV had been applied.

        Aircraft has departed too close.


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        Trigger

        The use case starts when the aircraft is at the runway holding point, ready to line up.


        Main flow

             1. The tower runway controller issues take-off clearance to a HEAVY leader aircraft.
                Tower runway controller uses the timer whenever needed behind HEAVY and MEDIUM
                aircraft in order to achieve the correct distance and time for the follower aircraft.

             2. Flight crew receive line-up clearance behind HEAVY departure.

             3. Flight crew can see the wind sock and check the direction of the crosswind.

             4. Flight crew lines up the aircraft.

             5. Tower runway controller checks that CREDOS is still available, reads the wind to the
                flight crew and gives the “ CREDOS “ take-off clearance to the flight crew via R/T.

             6. The flight crew releases the brakes, accelerates, rotates the aircraft and lifts off.

             7. The tower runway controller verifies that the aircraft has safely taken-off and is following
                the assigned standard instrument departure (SID) procedure, the speed constraints
                and/or the minimum climb rate.

             8. At the agreed point and/or altitude, the tower runway controller instructs the flight crew
                to transfer communications to the TMA departure controller.

             9. The use case ends when aircraft has contacted the TMA departure controller.


        Alternative Flows

        Alternative to step [2]. CREDOS is activated while aircraft subject to CREDOS is lining up

             10. Tower runway controller informs following aircraft that CREDOS is in use.

             11. Flight crew agrees to suspended separation.

             12. The use case resumes at step 4.

             13. Alternative at step [6] - aircraft stays 2 minutes or more on the runway and the benefit of
                 CREDOS is not achieved.

             14. The flow resumes at step 7

        Alternative to step [3] or [4]. Flight crew unable to accept suspended WV clearance

             15. The flight crew informs the tower runway controller that they want to apply ICAO WV
                 separation (or even additional spacing) instead of CREDOS.

             16. The tower runway controller will then not apply CREDOS suspension.

             17. Timer is used by the tower runway controller in order to achieve the correct ICAO WV
                 distance and time for the follower aircraft.

        Failure at step [2] or [7]. The first or second aircraft is deviating significantly from the departure
        procedure (SID route, speed constraint, minimum climb rate).


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             18. Tower runway controller detects that the leading or following aircraft is deviating
                 significantly from the flight trajectory planned according to the departure procedure
                 (route, speed constraint, minimum climb rate).

             19. RWY notifies the flight crew and if necessary issues a WV warning message to the
                 following aircraft and a correction of track/SID to leading /follower.

             20. The tower runway controller contacts DEP and informs of corrective actions.


        Failure flows

        The flight crew is not impacted by a failure of the CREDOS system.

B.4. HANDLE DEPARTING AIRCRAFT IN CROSS-WIND CONDITIONS

        Summary

        This Use Case describes how a TMA departure controller uses the system in order to be aware
        of crosswind reduced departures.


        Actors' roles

        TMA departure controller (primary) – wants to make sure that the aircraft climb on their
        dedicated SIDs in a safe manner with respect to the risk of collision with other traffic and wake
        vortex encounters - Has to take control of the aircraft from the tower runway controller after
        take-off. Wants to know when CREDOS is active/non active - Needs to know what SIDs are
        upwind/downwind, depending on the actual crosswind.

        Tower runway controller (support) – wants to make sure that the aircraft takes off in a safe
        manner with respect to the risk of collision with other traffic or obstacles and to maintain safe
        separation with other aircraft, – wants to optimise the sequence and the efficiency of the
        departure flow and the departure rate. – controls the first climb phase up to 2,500 ft. – needs to
        know what SIDs are upwind/downwind, depending on the actual crosswind.

        Flight crew (support) – has to climb and navigate the aircraft safely and efficiently.

        ACC supervisor (support) – wants to be informed of CREDOS being in use. – wants to make
        sure that CREDOS is used in a safe and efficient manner.

        Tower supervisor (offstage) – activates CREDOS operations.


        Pre-conditions

        TMA departure controller has been informed that CREDOS is in operation. A HEAVY departure
        has taken off and is already transferred to TMA departure controller while a follower MEDIUM is
        about to depart. CREDOS is activated and available.

        The transfer of responsibility for the MEDIUM take-off, between the tower runway controller and
        the TMA departure controller, is not completed. Flight crew is informed about CREDOS being
        used and has agreed to a suspended separation being applied. Tower runway controller has
        departed the MEDIUM aircraft 90 seconds behind the HEAVY.

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        Post-conditions

        Successful end state

        The system has correctly proposed CREDOS as being available and the tower runway
        controller as well as the TMA departure controller have correctly and safely applied it and the
        flight crew has complied with the clearances given. Where possible the runway rate has
        resulted in a higher number than the comparative ICAO WV rules would have resulted in.

        Failed end state

             -     Aircraft has not departed more efficiently than if ICAO WV had been applied.

             -     Aircraft has departed too close.

             -     Aircraft has departed on SIDs that were unfit for WV suspended separation.


        Trigger

        The use case starts when the MEDIUM aircraft is airborne and first appears on the TMA radar
        screen.


        Main flow

             1. TMA departure controller can see on a screen that CREDOS is activated and available.

             2. TMA departure controller monitors the navigation and climb of the HEAVY aircraft.

             3. TMA departure controller can see from the flight plan data which SIDs to anticipate for
                both aircraft.

             4. TMA departure controller anticipates the MEDIUM aircraft to be visible on the radar
                screen 90 seconds behind the HEAVY departure. The correct navigation on the
                assigned SID of the HEAVY is checked so that the MEDIUM doesn’t risk flying into a
                wake (generated by HEAVY) that could be transported by headwind or crosswind into
                the path of the follower.

             5. The TMA departure controller monitors the navigation and climb of the MEDIUM
                aircraft.

             6. The SID of the MEDIUM is now checked (see 4) so that the MEDIUM is not risking
                flying into a wake (generated by HEAVY) that could be transported by headwind or
                crosswind into its path.

             7. Communication is transferred from runway controller to departure controller and the
                flight crew will establish contact with departure controller.

             8. TMA departure controller will observe any indication of wind changes or flight crew
                reports that could affect the applicability of CREDOS. If necessary the CREDOS system
                can then be closed down immediately by the TMA departure controller so that the
                runway controller can go back to ICAO separations. An interface to do so is provided in
                the working position.




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             9. The Use Case ends when both aircraft are on correct SIDs and the correct radar
                separation is applied between them.


        Alternative flows

        Alternative at any step - flight crew reports wake encounter.

             10. TMA departure controller stops CREDOS.

             11. TMA departure controller informs tower controller about reason for stopping CREDOS.

        Alternative at any step - flight crew reports significant wind shift (direction and/or strength).

             12. TMA departure controller reports the wind shift to tower supervisor.

             13. Tower supervisor decides whether to maintain or stop CREDOS operations.

        Alternative at any step - The first or second aircraft is deviating significantly from the departure
        procedure (SID route, speed constraint, minimum climb rate).

             14. TMA departure controller detects that the leading or following aircraft is deviating
                 significantly from the flight trajectory planned according to the departure procedure
                 (route, speed constraint, minimum climb rate).

             15. TMA departure controller notifies the flight crew and if necessary issues a WV warning
                 message to the following aircraft and a correction of track/SID to leading /follower.

             16. TMA departure controller contacts runway controller and informs of corrective actions.


        Failure flows

        No failure flow is described from the perspective of the TMA departure controller. Potential case
        of wake turbulence encounter is addressed in alternative flows.




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C. CREDOS TOWER CONTROL SURVEY REPORT 2008
C.1. BACKGROUND
        The aim of the CREDOS project is to investigate the feasibility of relaxing the ICAO wake
        turbulence separation minimum that is normally required when aircraft depart immediately
        behind HEAVY or MEDIUM aircraft under certain crosswind conditions. It is proposed that the
        suspension of the separation can take place when there are sufficient cross winds to move the
        wake vortices out of the path of the following aircraft trajectory.

        One of the activities defined in the CREDOS Human Factors plan (Ref.1) is to investigate
        current practices at European airports. The purpose of this activity is to ensure that the
        CREDOS concept developers have a good understanding of ‘the current state of the art’ in
        terms of tower equipment, procedures and practice relating to wake vortex separation. As such,
        this activity will provide a better basis for the design of the CREDOS separation operational
        procedures and will also inform the development of the CREDOS concept as a whole.

        This annex to the CREDOS project Human Factors case deliverable presents the findings from
        the survey sent to a selection of European airports requesting information about their current
        procedures, equipment and practices concerning wake vortex separation.



C.2. METHODOLOGY
        The survey to investigate current tower equipment, procedures and practice relating to wake
        vortex separation was developed with the help of CREDOS concept developers, tower control
        operational experts and a Human Factors specialist. The survey included questions that
        covered areas of interest that had been identified through the Human Factors issues analysis
        (Ref. 1) and the stakeholder workshop (Ref. 2) held in November 2007. Thus the survey has
        two main areas of interest: 1) to understand the ‘state of the art’ in terms of the equipment and
        information available in European tower control centres today and; 2) to gain a better
        understanding of current European operational procedures and practice relating to aircraft
        separation.

        Twenty European airport/tower control centres were contacted via email and asked to
        participate in the survey. Nine of the twenty airports responded positively and completed the
        survey. The survey responses have been collated and are reported in this document. The
        majority of airports that have participated in this survey have asked for their responses to
        remain anonymous. As a result, no specific airport names are mentioned in this document.



C.3. SUMMARY OF FINDINGS
        Nine airports responded to the survey. The results indicate that the CREDOS concept and HMI
        development is strongly affected by local differences in terms of equipment, operational
        procedures and practices concerning wake vortex separation. The main impact on how
        CREDOS can be implemented comes from the differences in current HMI and practices. If for
        instance the current HMI is advanced and highly automated the HMI for CREDOS can also

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        include more advanced solutions. Another important impact on the benefits of introducing
        CREDOS is the differences in operation of the runways (segregated or not), the construction of
        the SIDs (distance to first turning point) and the current practices in applying the ICAO wake
        turbulence rules (only radar minima, delegation to flight crew). The main findings from the
        survey are described below.

C.4. IDENTIFIED DIFFERENCES BETWEEN AIRPORTS IN RELATION TO
   CROSSWIND DEPARTURES CONCEPT

        SID system

        In CREDOS it is foreseen that if the airport has SIDs that often diverge close to the runway
        there are further benefits that could be exploited when in crosswind conditions. By relaxing
        wake turbulence radar separation requirements on favourable SIDs this benefit can be realized.
        For instance a MEDIUM aircraft following a HEAVY that is turning upwind and away from the
        track of preceding very soon after departure could be exempt from wake turbulence separation
        requirements.

        All the larger airports surveyed use SIDs, in most cases, for all traffic. With P-RNAV and SIDs
        the predictability of what departing aircraft will actually do and where they will be increases.
        Precision in navigation is also improved the more detailed the SID is.

        The survey findings show that airports vary a lot in terms of the distance of the diverging point
        from threshold. Variations even occur locally depending on what runway direction is in use. One
        of the airports in the survey doesn’t have any published SIDs



C.5. TYPES OF SEPARATION OTHER THAN RADAR
        Other separation solutions providing higher possible departure capacity/throughput than radar
        separation are used but not applied in a coherent way across the airports. For example, three of
        the nine airports surveyed apply visual separation even for IFR flights when in good weather
        conditions.

        Off-track climb-out can be used in exceptional situations (i.e. go-around, emergency, equipment
        failure, CB-activity or activation of military or restricted sectors situated close to the runway) but
        is very rarely allowed as a standard for jet-engine IFR traffic due to environmental constraints.
        However, one of the nine airports surveyed did report that jet-engine traffic could be climbed off-
        track after passing 3,000 ft.



C.6. HOW TO MEASURE 2 MINUTES?
        In ICAO Doc. 4444 the runway wake vortex rule states that aircraft should be separated by 2
        minutes or more. However, ICAO has not provided guidelines on how to obtain or measure 2
        minutes. Depending on the airport we have found that the methods used to measure 2 minutes
        separation vary. There are reportedly two principle methods used to measure 2 minutes
        separation:


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             -     From start of roll until start of reading the take-off clearance;

             -     From lift-off to lift-off minus the estimated time it takes for number two to roll down the
                   runway.

        Variations of the two methods exist where the pilot reaction time from receiving the take-off
        clearance until the actual start of the take-off roll is estimated and also subtracted from the 2
        minutes. Rules of thumb are used in some towers, for example in one instance when tower
        controller sees on the radar that a certain distance out of the threshold has been past by aircraft
        number one, then aircraft number two can be released for take-off. One airport gives the timing
        responsibility to the flight crew by informing them of the wind and the aircraft type of preceding
        aircraft. Controllers don’t need to time at all. This is considered more efficient than 2 minutes
        timed by the runway controller, i.e. flight crews tend to depart earlier than 2 minutes in most
        cases when this method is applied.

        In the CREDOS project it has to be recognized that the present methods used to time 2 minutes
        separation vary and therefore might need to be changed in the local procedures if CREDOS is
        introduced, to ensure that the proposed benefits of CREDOS are achieved.



C.7. EQUIPMENT DIFFERENCES
        It is currently foreseen that CREDOS can be applied even in less advanced environments in
        terms of equipage but some of the more complex decisions the runway controller needs to
        make will be eased if more advanced equipment e.g. full A-SMGCS with multilateration and
        electronic strips, is installed. For example, electronic flight strips would enable some
        CREDOS-related information to be integrated e.g. information relating to a/c sequencing, SIDs,
        and the timings of departures.

        The airports survey varied in terms of the type of equipment that was available and used in the
        tower. Only three of the nine airports in the survey have full A-SMGCS including multilateration.
        Five of the nine airports reported having electronic strips. For the time being none of the airports
        in the survey has a DMAN. However, in order to apply even an advanced CREDOS HMI
        solution a DMAN is not deemed necessary. Electronic flight strips will be able to fulfil the
        CREDOS requirements.



C.8. APPLICATION OF ICAO RULES
        The application of ICAO rules also varied depending on the airport and/or country. One service
        provider applies 5 instead of 3 wake categories. In one of the countries surveyed, towers that
        use TMA air radar only apply the wake turbulence radar minima and not in combination with the
        wake turbulence runway separation minima as other European nations do. The latter method is
        similar to the way the rules are applied in USA. This relaxation of the 2-minute rule for the
        runway would give benefits in most cases as 5 NM radar separation is shorter than the radar
        distance when applying 2-minute separation on the runway. In CREDOS only the present three
        categories; HEAVY, MEDIUM and LIGHT are considered but more categories could easily be
        introduced as has already been done by one airport service provider. The application of radar


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        separation and no runway separation is very interesting for the CREDOS project and further
        exploration of this interpretation of the ICAO rules could be very useful in order to improve
        throughput at saturated airports.



C.9. COMMONALITIES RELATED TO CROSSWIND DEPARTURES

C.9.1. Tower controller responsibilities for radar separation
        5 of the 9 airports in this survey report taking on responsibility for more than just the runway
        separations. The extent of the additional responsibility taken on varies depending on the airport.
        This is interesting for the CREDOS concept for many reasons:

             -     CREDOS is a concept that concerns the phase of flight immediately after take-off and
                   therefore also the transition phase between tower and departure control. The further out
                   responsibility stays with the runway controller to achieve the airborne separation the
                   easier it is to suggest a non-ambiguous procedure and HMI for CREDOS;

             -     In the event of any safety concerns because of navigation error, system failure, etc. it is
                   also easier to design a robust procedure if only one controller role is involved.



        The major drivers for relocating responsibility from TMA control to tower control are:

             -     It is technically feasible nowadays because of daylight radar screens.

             -     Tower controllers often already have a radar rating for departures and arrivals.

             -     In the tower there is a safety net (looking out the window) which works in most weather
                   conditions (to a certain extent even in degraded conditions).

             -     TMA radar equipment has delays in the update rate that can be compensated for by
                   looking out the window if the control is provided from a tower.

             -     Multilateration used in A-SMGCS equipment at airports also provides excellent and
                   continuous surveillance of the initial climb phase.

             -     TMA radar equipment doesn’t always capture radar returns close to the ground. This
                   can also be compensated for by looking out the window when control is provided from
                   the tower.

             -     There is uncertainty as to where and when departures will actually be available on the
                   airborne radar radio frequency, so by letting tower maintain radio contact longer a
                   critical phase of flight is not disturbed by the handover procedure.

             -     Surface Movement Radar systems are able to capture airborne traffic closer to the
                   ground and with higher accuracy than TMA radar systems.



        From the results of the survey it seems as if the larger airports have moved towards delegating
        more and more of departure separation responsibilities from radar departure control to the tower



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        runway controller. This fits well with what is intended for CREDOS just after departure in the
        initial climb phase of flight.



C.10. MISCELLANEOUS
        None of the airports in the survey reported to be collecting data of the actual resulting time
        distance separation obtained between consecutive departures when the 2 or 3-minute wake
        turbulence separation rule is applied. This implies that it might be difficult to define a baseline
        against which comparisons can be made when a new separation is introduced, both in terms of
        efficiency and safety.



C.11. CONCLUSIONS


        The survey clearly shows that the differences between airports in terms of the equipment
        available and working practice as well as the difference in the interpretation of ICAO rules,
        depending on the country, make it difficult to develop one common concept. Therefore concept
        development for airports should remain high-level in the earlier stages of validation because of
        the local differences in terms of needs, infrastructure, procedures and equipment.

        The survey results also suggest that quick wins by promoting best practise and harmonised
        methods could lead to improved runway throughput and safety even without the introduction of
        CREDOS. As an example, the commonly applied suspension of runway wake turbulence
        separation in one of the countries when radar is used should be further discussed and
        investigated.

        Based on the survey results, it is now proposed that the CREDOS concept should describe the
        runway controller and not departure control in the TMA as being responsible for the airborne
        phase of flight immediately after departure. This approach also fits well with the existing
        procedures at many of the major airports that are believed to have the greatest advantages
        from introducing CREDOS. As five of the nine airports indicate that they could profit from
        reduced 3-minute separation when using intersection for departure, this aspect should be
        further investigated in the crosswind concept development.

        In the best interests of CREDOS, further field studies should concentrate on airports with two or
        more runways. A CREDOS concept based on visual separations would imply a major change to
        current procedures.

C.12. REFERENCES
      1. Validation          Strategy       and       Plan      (CREDOS           4.3).     CREDOS            Human        factors       Plan.
           CREDOS_421_ECTL_DLV_4-3_HumanFactorsPlan_28 01 2008_01.

      2. Minutes from CREDOS workshop Nov. 2007.




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C.13. COMPLETE RESULTS

C.13.1. Participating airports


        Airport ID                                 Size

        A                                          Medium

        B                                          Medium/Large

        C                                          Medium/Large

        D                                          Medium/Large

        E                                          Medium/Large

        F                                          Medium/Large

        G                                          Large

        H                                          Medium/Large

        I                                          Large




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 C.13.2. Tower equipment


Airport B               Airport B                Airport C                Airport D                Airport E                Airport F              Airport G           Airport H   Airport I

No SMR                  SMR                      SMR                      SMR                      No information           SMR and ATM            SMR                 SMR         SMR

No TMA Radar            Electronic strips        Electronic strips        Electronic strips                                 Electronic strips      Electronic strips   RVSM-SIDs   A-SMGCS with
                        planned for Dec                                                                                                                                            multi-lateration
                                                 Radar                    Radar                                             RWY        incursion   A-SMGCS             TMA radar
                        2008
                                                                                                                            alert                                                  RWY     incursion
                                                 Information              TFDPS terminal                                                           RIMCAS
                        A-SMGCS                                                                                                                                                    alert
                                                 System                   flight     data                                   Wind / met. Data
                        (multilateration)                                                                                                          AFDAS
                                                                          processing                                        integrated    in                                       Choice of TMA
                        planned for June
                                                                          system                                            SMR display                                            radar, SMR or
                        2008
                                                                                                                                                                                   combi-display on
                                                                          IDVS      system                                  Other (but other
                        TMA         radar                                                                                                                                          screens
                                                                          depicting     the                                 not specified)
                        screens in TWR
                                                                          weather data
                        MET     data   in
                        separate screens

                        Other           (not
                        specified)




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C.13.3. Runway configuration and information

        Airport A

        Two diverging runways. Used in mixed mode.


        Airport B

        Three runways, two independent parallel and one diverging. Used in segregated mode.


        Airport C

        Two runways. Most of the time segregated.


        Airport D

        Three runways. Two parallel and one crossing. Most of the time segregated.


        Airport E

        Two parallel runways and a crossing runway. Segregated mode.


        Airport F

        One runway. Mixed mode.


        Airport G

        Two independent parallel runways. Segregated mode.


        Airport H

        Crossing dependant runways. Mixed mode.


        Airport I

        Five runways. Segregated mode except in strong wind conditions.



C.13.4. Procedures for changing runway configuration

        Airport A

        Responsible: aerodrome control, in consultation with radar control.

        Procedures: ILS on two of the four landing directions only, no switching required. Strips only
        change in terms of runway annotation. Lighting is under responsibility of aerodrome control and
        is selected as appropriate.


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        Changeover verification: last movement off the old runway is co-ordinated as such, similarly the
        first movement on the new runway in use.


        Airport B

        Responsible: watch supervisor.

        Procedures: all systems are considered when changing RWY. This is described in checklists.

        Changeover verification: coordination with all operators and with the tactical supervisor at the
        ATCC


        Airport C

        Responsibility rests with both aerodrome and approach control. Close coordination is necessary
        and applied. A change will normally be initiated by aerodrome control. The ILS is operated
        directly by the tower controller, Flight Plan Data System is operated by the tower assistant,
        strips are no longer used. Aerodrome lighting is operated by the tower controller, ATIS will be
        broadcasted automatically, based on the automatic weather information display system. This
        system is operated by the assistant of the tower controller.

        Direct verbal coordination between tower and approach control. Airport operator is informed by
        telephone.


        Airport D

        Responsible: tower controller.

        Procedures: ILS, strips, RVR (runway visual range), lighting is automatically changed by lighting
        system. ATIS will be done automatically by the end of 2008.

        Changeover verification: elbow co-ordination with tower crew, co-ordination with director via
        squawk box.


        Airport E

        Responsible: tower supervisor

        Procedures: Once the need to change configuration is determined, the TWR supervisor agrees
        with the TMA supervisor the moment of the change (how long to the change, how many acft will
        still land/depart in the present conf, which are the first arr and the first dep in the new conf). The
        supervisor, possibly with the help of another ATCO in the role of coordinator, makes sure that
        all the steps related to the change are followed (ILS, strips, lighting, ATIS, etc.).

        Changeover verification: It is the supervisor's responsibility to inform the ATCOs and receive
        their acknowledgement of any change that is made, and they have to follow the procedure as
        instructed (change taxiing routes, change SIDs for new dep rwy, use of stop bars, etc.)


        Airport F



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        Responsible: ATC watch supervisor and Terminal Control Group Supervisor Airports agree a
        change over Terminal Control (TC), the name of the unit which provides the approach function
        for all TMA airports. The Group Supervisor is responsible for tactical decisions affecting 5
        airports.

        Procedures: a check list is followed.

        Changeover verification: by means of tick items on a check list.


        Airport G

        Responsible: ATC Supervisor .

        Procedures: checklist followed by the tower supervisor.

        Changeover verification: using the checklist.


        Airport H

        Responsible: RWY controller after coordination with APP/TMA controllers.

        Procedures: ILS change coordinated with Technical Control Desk; automatic SID change for
        the new strips/manual SID change for the existing strips; RWY Approach lights change; wind
        display change.

        Changeover verification: Regarding the controllers the change is obvious as there is radar
        environment at the TWR and APP. Also all controllers currently working are in the loop during
        the change. The information on the rwy in use is spread among different systems (radar display,
        meteo info, wind analogic display, strip bays, etc.).


        Airport I

        Responsible: TWR & APP supervisors.

        Procedures: The RWY combination is changed in the system, allocation for specific flights is
        automatic or by hand (specific steps are: determine the actual time of RWY change, send new
        traffic to the new RWY combination, manually handle other traffic during a specific transfer
        period). Lighting is changed manually; updating the ILS: there is no automatic system for
        checking ILS configuration/availability.

        Changeover verification – Manual co-ordination & system display (MRI – main RWY indicator)

C.13.5. Crosswind information

        Airport A

        No.


        Airport B

        Yes, on MET system screen



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        Airport C

        Wind direction and speed are measured at two different points, located close to the threshold
        areas. Both items of information are displayed to the controller on a monitor in front of him,
        including the actual head and crosswind components in regard to each landing direction.


        Airport D

        Crosswind information/components provided via a display system.

        Crosswind information is specific to each runway. Displayed in digits, updated every 10
        seconds.


        Airport E

        We have an Integrated Meteorological System in every control position and TWR Control
        Integrated Position. It is a screen that displays wind and other important instant data specific for
        each rwy. Info is available at a glance for any controller on duty.


        Airport F

        Crosswind component tables are available in a data retrieval system at all ATC positions. The
        information is not specific to each runway. It is displayed in tabular format to the controllers.


        Airport G

        No crosswind indication. Traditional wind indicators are available at every working position.


        Airport H

        No crosswind indication.


        Airport I

        Crosswind information is displayed in digital format on the CCIS-info-system (in numbers only,
        either tabular or on the RWY config layout diagram).



C.13.6. Separation procedures – SID divergence

        Airport A

        N/A - no SIDs at this airport.


        Airport B

        Different from each runway, but the earliest a SID can diverge from each rwy is between 0.5
        and 3 NM. There is no possibility for controllers to change SID in order to separate aircraft
        earlier. Off-track departures are used for smaller aircraft in order to separate aircraft earlier.

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        Airport C

        Some departures from RWY XX have to make a right turn at approximately 1 NM after take-off.


        Airport D

        Controllers are not able to change SIDs in order to separate aircraft earlier.

        Off-track departures for smaller aircraft are used to separate aircraft earlier but only for props
        less than 5.7 tonnes in VMC conditions


        Airport E

        5.5 NM for rwy XX Left; 7 NM for rwy XX Right.

        We cannot change the SIDs for environmental reasons. We just can change the departure
        sequence so that we can optimize the dep's interval. We do not use off-track departures for
        smaller aircraft for the same reason as above. We have to stick to the SIDs, because they are
        the only "environmentally-friendly" manoeuvres.


        Airport F

        Minimum is not specified. However the earliest published SID divergence is at a DME 1.0 for 4
        SIDs. Controllers cannot change SIDs in order to separated aircraft earlier. Off-track departures
        for smaller aircraft are not used to separate a/c earlier. For northbound SIDs the earliest altitude
        to vector away from the SID is 3,000 ft - all others are 4,000 ft. At night for all SIDs it is 4,000 ft.


        Airport G

        2 NM. Deviation from SID is allowed only in special circumstances related to safety and
        emergency situations. No off-track climb-out for smaller aircraft. Ac can be deviated after 4,000
        ft by terminal control.


        Airport H

        Earliest point for SIDs to diverge is at 2,000 ft. 4 NM approximately from runway end.


        Airport I

        Off-track departures used 500 ft for propeller jets and 3,000 ft for jets.

C.13.7. Separation procedures – tower controller separation responsibility

        Airport A

        RAD will give a release for all IFR departures and aerodrome control will then depart aircraft in a
        manner which fits this release and other non-IFR traffic. This is done visually or with the aid of
        ATM. ATM support is needed.




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        Airport B

        Tower controller is responsible for separation in all cases. TMA radar is used and departure
        given based on a/c type, weather and experience. The separation is followed on radar, level
        restriction sometimes given. Speed restriction is given below FL 100 (250 kt). Also visual
        separation between SID and headings. TMA radar and ground movement radar is needed.


        Airport C

        Tower controller retains responsibility until all the departing aircraft pass 2,000 ft. The aircraft
        has to remain on the frequency of aerodrome control until passing 2,000 ft. This procedure is
        published in the departure route. Frequency change will take place without any special
        instruction or notice. Aerodrome control is thus able to instruct aircraft to fly any necessary
        procedure if caused by overshooting aircraft or other reasons.


        Airport D

        Tower controller is responsible for airborne separation in all cases. How it is achieved depends
        on the performance of the aircraft. The tower controller has to remain with the following
        departure to ensure that separation exists until reaching the initial altitude, which is 5,000 ft on
        all departures (check). Radar support is needed.


        Airport E

        The TWR controller is responsible for airborne separation in all cases. The TWR manages its
        traffic without depending on previous coordination with APP controllers. We don't report "ready"
        or wait for the "release" of any traffic. We give the airborne separations according to the tables
        included in the letter of agreement with approach control. In those tables there are 2 parameters
        to establish separation: distances (in NM) or their approximate equivalences in minutes. We
        need the support of the approach radar and a clock (and the controllers' skills, of course).


        Airport F

        Yes tower control is responsible for airborne separation in all cases. Time and distance for
        departures and reduced separation in the vicinity of the aerodrome as published in the State
        ATC instructions. Further separation minima are specified for one SID, however, where
        standard vortex wake separation is greater this is applied. Support / equipment needed - ATM
        and clock. (ATM aerodrome traffic monitor. A radar display typically set at a range of 35 NM).


        Airport G

        Tower control is responsible for departure separation in all cases. ATM (Aerodrome Traffic
        Monitor) is used, sometimes aided by visual contact.


        Airport H

        Tower control is responsible for just some separations. It is done after coordination with
        approach control.

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        Airport I

        TWR control is responsible for airborne separation in all cases except when DEP gives
        clearance for a departure, which rarely happens. TWR is responsible for initial separation.
        Exceptions to this are lvp and parallel departures. Support needed includes visual control,
        procedures, TAR display, SMR, R/T.

C.13.8. What ICAO airborne separation rules are applied for departures?

        Airport A

        All types of separation are applied, depending on the situation.


        Airport B

        Radar, procedure and visual.


        Airport C

        Normal radar separation minima, same as applied by departure control.


        Airport D

        Airborne separation is mainly based on radar minima, only sometimes on vertical separation.


        Airport E

        Radar minima.


        Airport F

        Speed tables based on time and also distance spacing based on controller training in advanced
        use of the ATM as specified in unit instructions.


        Airport G

        Diverging track separation is most common. Otherwise time separation on same route. 5miles
        radar separation may be used on similar types on same route.


        Airport H

        Wake turbulence separations


        Airport I

        All, i.e. radar minima, procedure, lateral, vertical, visual – used often in combination. More
        specific: visual, geographical and procedural (track separation, time separation)




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C.13.9. What is the radar minimum separation required for a MEDIUM
   aircraft following another MEDIUM on the same SID?


Airport A      Airport B      Airport C      Airport D       Airport E      Airport F      Airport G       Airport H      Airport I



3 NM           4 or      5    3 NM           3 NM            5 NM           3 NM           5 NM            5 NM           3   NM
               NM                                                                                                         TMA but
                                                                                                                          5 NM for
                                                                                                                          CTA

        Are some separation modes dependent on visual conditions?


        Airport A

        IFR vs VFR, visual separation between two successive IFR departures


        Airport B

        No


        Airport C

        No


        Airport D

        Yes, the use of off-track climb with LIGHT aircraft.


        Airport E

        No


        Airport F

        No specific "modes".


        Airport G

        In visual conditions visual separation is used until the turning point (usually not further out then
        3 Nm)


        Airport H

        Only if the RWY controller provides the separation and after first coordinating with departure
        control.



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        Airport I

        Visual separation is used to increase capacity with different SIDs etc.

C.13.10. Working practice
        Handover of departing traffic from tower to departure.


        Airport A

        Departures are generally transferred at around 1,000 ft.


        Airport B

        Handover takes place when there is no longer a separation issue.


        Airport C

        Frequency change and transfer of control is effected when the departing aircraft passes 2,000
        ft.


        Airport D

        All departures switch frequency when passing 2,000 ft, as published in the SIDs. This is also the
        moment of transfer of control.


        Airport E

        Departing aircraft are handed over from tower to departure control as soon as the acft is
        airborne.


        Airport F

        Transfer of frequency and control takes place as soon as the tower controller has checked the
        code call sign conversion is correct and the required minimum separation from the preceding
        aircraft exists. There is a published instruction that transfer should take place as soon as
        possible. In practice, controllers do not transfer an aircraft until it has passed 1500 feet agl in
        order to give the crew time to complete some of the immediate after-departure checks to retain
        control in the event of a go-around when operating high intensity runway operations and to
        confirm the aircraft is established on the correct track before departing another aircraft.


        Airport G

        When established in the first turn of the SID, not in conflict with other departures and when it
        has passed 3,000 ft climbing (no longer a factor in the case of missed approaches)


        Airport H

        When airborne and passing 1,000 ft.


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        Airport I

        At 200 ft unless otherwise instructed. The reason for this is to reduced TWR RT load.***



C.13.11. Procedures for achieving 2 and 3-minute wake turbulence
   separation compared to ICAO Doc. 4444
        In one country if radar procedures are used by tower control no wake turbulence runway minima
        in terms of time are used, as runway controller wake turbulence radar separation minima only
        are applied. One ANSP applies 5 weight categories instead of the three ICAO categories when
        determining radar and time distances. One country reports having a special rule for B737 800.


        Airport A

        No difference


        Airport B

        There is no description on how to achieve it. All controllers are taught this during training.


        Airport C

        We just apply the minima for radar separation, valid for wake turbulence separation, because
        radar facilities are continuously available. According to the procedures, separation based on
        time has to be applied only if radar facilities are not available.


        Airport D

        The manual procedures state a minimum wake turbulence distance between departures of 4, 5
        or 6 NM – as long as radar is available and used. Only in cases when radar is not available is
        separation based on time. However it is known to staff that pilots have the rule of 2-minute
        separation when departing behind a HEAVY aircraft. After local investigation of three bigger
        airlines, it was established that 2-minute separation is simply good practise, based on the
        non-radar separation minima, and not a rule. One airline reported that the company rule was
        that flight crews have to wait 2 minutes in all wind conditions.


        Airport E

        Apply the same rules as those in the 4444 Document. Apart from the general rules, the Civil
        Aviation Authority considers the Boeing 737-800 to be HEAVY when preceding another acft,
        and as MEDIUM when following another acft.


        Airport F



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        The spacing between aircraft determined either by time or distance is to be applied so that
        aircraft of a lower weight category do not fly through the wake of an aircraft of a higher category
        within the area of maximum vortices. UK vortex wake categories differ from the categories used
        for flight plan purposes.


        Airport G

        The same as in Doc. 4444. No special guidelines on how to achieve this.


        Airport H

        As in Doc. 4444.


        Airport I

        Inform departing a/c of wind and type of preceding a/c leave timing to the aircrew. Otherwise
        time 2 or 3 minutes



C.13.12. How do controllers achieve 2-minute separation?

        Airport A

        Timing taken from when first aircraft is seen to commence its take-off roll.


        Airport B

        By using a clock.


        Airport C

        Not applied


        Airport D

        Based on a digital clock installed at the working position.


        Airport E

        With the clock.


        Airport F

        By timing the interval between successive departures in seconds.


        Airport G




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        When first aircraft passes the 2Nm mark on the radar display the next aircraft will get cleared for
        take-off.


        Airport H

        Visual observation of the clock at the working position and marking on strips.


        Airport I

        Inform departing a/c of wind and type of preceding a/c, leave timing to the aircrew. Otherwise
        time 2 or 3 minutes.



C.13.13. What measuring points are used to ensure 2-minute separation?

        Airport A

        Timing taken from when first aircraft is seen to commence its take-off roll.


        Airport B

        Lift off.


        Airport C

        Not applied.


        Airport D

        2 minutes after aircraft number one starts moving, take-off clearance is given to aircraft number
        two.


        Airport E

        We assume, according to our statistical records, that the time between the take-off clearance
        and the acft lifting off varies between 30" and 60". We accordingly observe the lift-off of the
        preceding acft, and at this point we start counting. 90 secs after, we issue the take-off clearance
        to the next acft, so that its lift-off will take place between 120" and 150" after the lift-off of the
        preceding acft.


        Airport F

        The 2-minute is measured from the time the nosewheel of the departing aircraft lifts. The roll
        time of the following aircraft is taken into account when issuing its take-off clearance.


        Airport G



EUROCONTROL                                                                                                                  Page 94

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        2 minutes starts when the first aircraft rotates. We assume a take-off roll of 45 seconds and give
        take-off clearance after 1 minute 15 seconds. Pilot reaction time is normally anticipated within
        the 2-minute period – and this includes the pairing of the aircraft types, and airlines involved.


        Airport H

        From the time the first aircraft moves until next take-off clearance is given and read back.


        Airport I

        Not aware of measuring points other than clock if the controller times (rarely).

C.13.14. How do you register time to ensure 2-minute separation is
   achieved?

        Airport A

        Use the clock in front of controller.


        Airport B

        Noting take-off time on strip and monitoring the clock.


        Airport C

        Not applied.


        Airport D

        Keep the time movement of first departure in mind and clear second aircraft for take-off 2
        minutes later.


        Airport E

        Uses the clock. Writes down in the strip the time when the acft is airborne and uses this as
        reference to issue the clearance to the next acft.


        Airport F

        Where vortex separation is required, the controller will click the "airborne" box on the electronic
        flight progress strip when the nosewheel lifts, this time is displayed on the strip in minutes and
        seconds.


        Airport G

        Marking electronic strips which records minute and seconds for the airborne time.


        Airport H


EUROCONTROL                                                                                                                  Page 95

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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION


        Marking the strips.


        Airport I

        If departure is timed, using a clock and marking the strip.

C.13.15. Timer equipment

        Airport A

        Clock is integrated into ADIS screen. It is used for recording actual times of aircraft movements,
        determining whether pushback approval is appropriate in relation to departure restrictions, time-
        line in the event of emergency, recording items relevant to log-keeping.


        Airport B

        In all positions in front of the operator.


        Airport C

        Not used.


        Airport D

        Every working position has its own digital clock right in front of the controller. Additionally there
        are different systems with an integrated clock. The clocks are mainly used to establish a given
        departure-interval based on time or to meet the slot of departure. Timer not available.


        Airport E

        We have one clock in the tower integrated working position and another in the radar display.


        Airport F

        E-strips cannot display different line-up points dynamically at airport F.

        3 clocks showing hours minutes and seconds are available to the ARWY controller (electronic
        flight strip display, SMR display and ADIS (Airport Display Information System) displays weather
        and other information. A clock forms part of the display.


        Airport G

        Clock is available on the weather display screen and on the electronic flight strip display. When
        a strip is moved to the airborne bay, airborne time is registered automatically.


        Airport H

        Just a clock in the working position.



EUROCONTROL                                                                                                                  Page 96

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        Airport I

        Clock is available on the main displays. Used mainly for VFR, ATA & ATD.



C.13.16. Are working methods commonly applied?

        Airport A

        Commonly applied.


        Airport B

        Commonly applied.


        Airport C

        Not applied.


        Airport D

        Yes, the methods described above are commonly applied.


        Airport E

        Commonly applied, although some controllers may use equivalent distance references, such as
        issuing the take-off clearance when the preceding a/c is between 3 and 4 NM out.


        Airport F

        They are commonly applied.


        Airport G

        Commonly applied.


        Airport H

        Individual.


        Airport I

        They are common.

C.13.17. What is the average real separation time between aircraft
   (MEDIUM behind HEAVY) when 2 minutes is applied in a queue
   situation?

        Airport A

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        2 minutes.


        Airport B

        Very close to 2 minutes.


        Airport C

        Not applied.


        Airport D

        Close to 2 minutes.


        Airport E

        It doesn’t make any differences whether it is a queue situation or not. Between 6 and 8 NM.
        (Due to the consideration of the 737-800 as HEAVY, the majority of our wake turbulence
        separations consist in a MEDIUM traffic following a B738. Despite that, some pilots, especially
        those of non-local operators, refuse the 2 minute separation, accepting the 3 NM=1 minute
        interval after a B738).


        Airport F

        From the same departure point 2 minutes, from an intermediate departure point, 3 minutes.
        Some controllers are able to achieve this to within 3 seconds. In LVPS where airborne reports
        from pilots are the trigger, then the separation probably increases to an average of 30 seconds
        to 1 minute more.


        Airport G

        Close to 2 minutes but in reality maybe just under 2 minutes if you have a light MEDIUM
        following a HEAVY. No real data is available.


        Airport H

        2 min or more.


        Airport I

        Approx. 2 minutes as timed by aircrew.

C.13.18. When applying 2-minute what is average radar spacing achieved if
   aircraft speeds are fairly equal?

        Airport A

        5 NM.


EUROCONTROL                                                                                                                  Page 98

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        Airport B

        5.5 NM.


        Airport C

        Not applied.


        Airport D

        About 7 NM initial separation.


        Airport E

        Between 6 and 8 NM.


        Airport F

        6 NM, subjective estimate based on today's departures. It is difficult to assess without a
        structured study because it was not possible for me to know at what point the radar controller
        cancelled speed control restrictions for the preceding aircraft.


        Airport G

        Usually more than 5 NM.


        Airport H

        Around 5 NM.


        Airport I

        6 NM.

C.13.19. Radar spacing when both aircraft follow the same SID

        Airport A

        Close to 5 NM                      usually

        Less than 5 NM                     occasionally

        More than 5 NM                     occasionally


        Airport B

        Close to 5 NM                      90%

        Less than 5 NM                     2%

        More than 5 NM                     8%


EUROCONTROL                                                                                                                  Page 99

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                                FINAL CONCEPT OF OPERATIONS DESCRIPTION


        Airport C

        Close to 5 NM                      often

        Less than 5 NM                     often

        More than 5 NM                     seldom


        Airport D

        Close to 5 NM                      15%                  60%

        Less than 5 NM                     5%                   10%

        More than 5 NM                     90%                  30%


        Airport E

        Close to 5 NM – We give a 5 NM spacing between acft following the same SID if NO wake
        turbulence separation is needed.

        Less than 5 NM – Only in cases that NO w.t.s. is needed and the acft follow different SIDs.

        More than 5 NM - If wake turbulence separation is provided, the spacing between 2 departing
        acft is ALWAYS more than 5 NM.


        Airport F

        Slightly more than 5 NM when 2-minute is applied between same types on the same SID.


        Airport G

        Close to 5 NM                      40%

        Less than 5 NM                     40%

        More than 5 NM                     20%


        Airport H

        Close to 5 NM                      100%


        Airport I

        Close to 5 NM                      very often

        Less than 5 NM                     rarely

        More than 5 NM                     regularly



        Miscellaneous




EUROCONTROL                                                                                                                Page 100

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C.13.20. Is data available from the Surface Ground Movement radar (SMR)
   to check the time between first and second aircraft’s cleared for take-off
   in peak hour?

        Airport A

        No SMR at this airfield.


        Airport B

        No data is not currently available, could probably be available with software update.


        Airport C

        Data are not available, take-off clearance for succeeding aircraft will be issued upon controller's
        judgement to ensure wake turbulence separation minima. Data will depend on aircraft type and
        company.


        Airport D

        No, SMR is an analogue radar.


        Airport E

        We don't have an SMR.


        Airport F

        No data is currently available and probably could not be available because we assess it from
        the time the nosewheel lifts on departure. In low-visibility procedures the pilot is requested to
        report airborne and the clock is started from the time of this transmission.


        Airport G

        No data is available. It could probably be obtained, but would involve substantial work effort.


        Airport H

        No.


        Airport I

        No, but it could be extracted for investigation purposes.




EUROCONTROL                                                                                                                Page 101

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C.13.21. If wake turbulence separation (3-minute rule) was suspended when
   using intersection would you then be likely to use intersection
   departures more frequently?

        Airport A

        No.


        Airport B

        Yes.


        Airport C

        Because of the airport layout, this does not make a great difference. It wouldn't help us really.


        Airport D

        No.


        Airport E

        We don't use intersection departures very often. Anyway, according to experience in the past, I
        would say "yes".


        Airport F

        Yes.


        Airport G

        Yes.


        Airport I

        Only if deemed safe (obviously), and if separation is equal to full-length departure




EUROCONTROL                                                                                                                Page 102

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C.13.22. If in the future the separation between departures was lower than
   current separation minima – how could you measure it? How could you
   prove that the required spacing from runway to airborne was achieved?

        Airport A

        Knowledge of aircraft performance and a clock.


        Airport B

        Don’t know, needs to be measured by radar system.


        Airport C

        The tower controller is able to apply any separation minima for departing aircraft you want. You
        can make it from 1 NM to 10 NM, this will be no problem for him. Limiting factors are wake
        turbulence separation minima and radar separation minima required by departure control.


        Airport D

        Since the radar separation between all departures is based on miles, a change of the rules
        wouldn’t make a difference to the working procedures.


        Airport E

        We would use the same tools we use today: radar and clock. And in a year or so we will have
        SMR, and in 2 years we will have multilateration.


        Airport F

        In answer to both questions, and with current technology, we would still continue to measure it
        in time.


        Airport G

        Using time data from e-strip system.


        Airport H

        Need of a specific tool to achieve it.

        Another method is also possible: in the case of winds with a crosswind component that exceeds
        12 or 13 knots of lateral wind, the controller can always tell the pilots the wind and ask them to
        report ready in case they request wake turbulence separation. Usually, this procedure results in
        a shorter spacing between departures than if the 2-minute gap had been applied.




        Airport I

EUROCONTROL                                                                                                                Page 103

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        The principles / measurement / guarding of separation does not depend on time or distance
        needed. Future capacity however, is threatened by the dependent runway system.

        At our airport, WT separation for departures is generally obtained by giving pilots info. about
        preceding a/c and wind and leaving timing to them (or letting them report ‘ready’ and timing their
        departure on other traffic). Efficiency is obtained through the above procedure (usually less than
        2 full minutes), clustering heavies and optimising the use of intersections. No tool is available
        other than looking at radar.




EUROCONTROL                                                                                                                Page 104

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