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					                                RTCA SC-214/EUROCAE WG-78
                Air Traffic Services Safety and Interoperability Requirements
                                                   General Information
Paper Reference:                                   Revision:             Date:            Status :
                                                           0.1             09 September
POS-PL-NAT CNSG4                                                               2011
                                                                                          Configuration Sub-Group
Issue Response
Editor / Author:                                   Review Meeting/Teleconference:
Thierry LELIEVRE (ALTRAN) CSG Co-Chair             Comments Due: ASAP
SC214/WG78 Coordinator

Position Paper Title:
SC214/WG78 CSG Response to NAT Issues
Abstract and Proposed Action:

SC214/WG78 – ICAO NAT ATMSG & CNSG has been established in order to take benefit of Oceanic FANS
data link experience in the definition of Advanced Data Link Application and Services to support future Data
Link Oceanic/Continental Operations.

In this context of coordination, ICAO NAT Groups have submitted to SC214/WG78 a list of data link issues (see
NAT CNSG4 WP09 SC214_WG78.pdf & NAT ATMG 37 Final.doc). This position paper presents the
SC214/WG78 response to these issues.

It has to be noted that some issues are still under discussion in SC214/WG78. Final SC214/WG78 Position will
come later.

Meanwhile, SC214/WG78 recommends NAT Groups to review the current CPLDC message Set.

Key words (Optional):
ADS-C capability impaired

SC-214/WG-78Groups              Additional Names                 Additional Names          Additional Names

CSG                             NAT CNSG
VSG                             NAT ATMSG
                                 NAT ATMSG & CNSG Issues
                                                                                                                  SC214 / WG78 Response
                                                                                    Any other
Contributor          Problem/gap                      Suggestion
LHA           Specific behavior regarding     Homogeneity in avionics      We shouldn't need to know the      Maximizing the homogeneity in avionics
              handling of CPDLC               behavior and reliable and    type of aircraft to know how it    behavior is one priority of the
              messages and ADS contracts      affordable method for        behaves. In many cases the         SC214/WG78 SPR / INTEROP
              highly affected by numerous     updates.                     variability in implementation      document. Nevertheless during the
              types and sub-types of                                       totally negates the value of the   transition path to the future avionics,
              avionics                                                     function.                          numerous types and sub-types of avionics
                                                                                                              behavior will still have to be handled.

LHA           Uncertainty regarding           Timely and accurate          It is equally important to know    The SC214/WG78 SPR/INTEROP
              whether or not messages         message assurance.           whether the message has been       Standards are ATN Compliant which
              have been received or not                                    delivered or not.                  allows the use of Logical
                                                                                                              Acknowledgement (LACK message).
                                                                                                              These standards provide the definition of
                                                                                                              environments where LACK is required
                                                                                                              (LACK Environment) and where LACK
                                                                                                              is not required (NO LACK Environment).
                                                                                                              New capabilities/message exchange
                                                                                                              (UM233) during the CPLDC Connection
                                                                                                              Establishment allows the ground system
                                                                                                              to declare what is its environment and to
                                                                                                              configure the avionics in consequence.

LHA           Avionics’ handling of           Universally available        The need for defining a            Like the existing SPR/INTEROP
              “latent” messages delivered     latency timer as a network   maximum “lifetime” of a            standards, used today, the Latency Time
              by one ANSP can be affected     function                     message may change over            Check (LTC) function is a mandatory
              by decisions of previous                                     time; it may also vary from        capability in the SC214/WG78
              ANSP. Support for this                                       unit to unit (or indeed from       SPR/INTEROP Standards, driven by a
              function varies from aircraft                                message to message). It would      safety requirement.
      to aircraft which largely                                   therefore be better to make this   Note: Current ATN-B1 aircraft systems
      destroys its value.                                         a parameterized network (i.e.      have a hard-coded value of 40s set in the
                                                                  messaging) function rather         aircraft. Existing FANS 1/A+ aircraft
                                                                  than an avionics function.         implementations receive a free text
                                                                                                     The Ground system must set-up the
                                                                                                     required Latency Time Value which has
                                                                                                     to be used by avionics for LTC.
                                                                                                     In the SC214/WG78 standards, this value
                                                                                                     is provided by sending UM340 during the
                                                                                                     CPLDC Connection Establishment. All
                                                                                                     avionics are required to support the LTC
                                                                                                     When no value is provided then a default
                                                                                                     value is set-up (999sec) by avionics. It has
                                                                                                     to be noted that UM340 could be sent at
                                                                                                     any time by the ground system to set-up a
                                                                                                     LTC Value.

LHA   Difficult to detect aircraft   Implement a vertical rate    This is different from the         SC214/WG78 Standards define the
      leveling prior to reaching     event, where ADS-C report    altitude range event, which        Vertical Speed Change Event. The
      assigned flight level.         is sent when vertical rate   only detects if the aircraft       Vertical Speed Change event is triggered
                                     decreases through a          strays outside the range           If the magnitude of the vertical speed is
                                     specified threshold                                             greater than the higher bound our less
                                                                                                     than the lower bound. The ADS-C
                                                                                                     Report, containing the Ground Vector and
                                                                                                     the Vertical Speed Change event
                                                                                                     Indication is sent once every minute
                                                                                                     whenever the magnitude of the aircraft’s
                                                                                                     vertical speed is greater than the higher
                                                                                                     bound or lower than the lower bound. The
                                                                                                     aircraft ceases sending ADS-C reports
                                                                                                     when the magnitude of the aircraft’s
                                                                                                     vertical speed returns to a value between
                                                                                                     or at the bounds
STC   Ground system “assumes”         Have a fully qualified         Unforeseen network delays of       The timestamp of each report shall be
      and inserts a date and hour     date/time inserted from        messages may result in             compliant to ICAO Annex 11
      for ADS-C reports.              FMS into all ADS-C             receiving systems making false
                                      reports.                       assumptions about the absent
                                                                     high-order components of

STC   Ground system doesn’t know      Just before terminating the    Suggested text: [aircraft ident]   This is FANS Issue.
      when aircraft terminates the    CPDLC connection, have         TERMINATING CPDLC                  The SC214/WG78 SPR/INTEROP
      connection                      the avionics automatically     CONNECTION                         Standards are ATN Compliant which
                                      send a downlink message                                           requires the user to be notified of
                                                                                                        termination of the CPLDC Connection.

STC   Ground system doesn’t know      When new CDA                   Suggested text: CPDLC              The SC214/WG78 SPR/INTEROP
      when it has become the CDA      established, have the          CONNECTION                         Standards are ATN Compliant which
                                      avionics automatically send    ESTABLISHED WITH                   requires the aircraft to send the DM99
                                      a downlink message.            [aircraft ident]                   CURRENT DATA AUTHORITY when
                                                                                                        the CPLDC Connection becomes active

STC   Depending on the order the      Ensure that, in the case       Maybe it would be possible to      This issue is still under discussion in
      ADS-C contracts were            where multiple ADS             somehow identify to the ADS-       SC214/WG78. This is more a network
      established, it can take some   connections are established,   C system that the current          issue rather than an Avionic issue.
      time for the current control    that ADS reports are sent      controlling ATSU is?               Nevertheless Avionic change may
      authority’s turn to come        FIRST to the CDA (if there                                        contribute to mitigate it. Different
      when reports are being sent     is also a CPDLC                                                   alternatives are under assessment.
      to multiple addresses.          connection).                                                      Nevertheless SC214/WG78 first approach
                                                                                                        recommends not bringing more
                                                                                                        complexity in ADS-C management and to
                                                                                                        keep ADS-C independent from other Data
                                                                                                        link applications (CDA being a status
                                                                                                        managed by CPLDC).
                                                                                                        In the context of future use of data link
                                                                                                        (e.g. 4DTRAD Environment), the high
                                                                                                    priority may be allocated to a ground
                                                                                                    other than the CDA. In consequence
                                                                                                    criteria used to allocate the priority is not
                                                                                                    so obvious.
                                                                                                    In addition, and beyond this CDA Issue,
                                                                                                    the RCP applicable to ADS-C may not be
                                                                                                    met in some circumstances.
                                                                                                    RCP/Performance for ADS-C may have
                                                                                                    to be reconsidered.

STC   Because others may set up     Highest priority connection   As an alternative, allow          As defined in SC214/WG78 Standard,
      ADS-C connections without     for CDA, next for NDA,        ground units to query avionics    when all ADS-C slots are allocated to
      coordination, ATSUs who       next for previous CDA – if    as to identity of other holders   grounds, ADS-C shall reject a new
      need the ADS-C connections    necessary, disconnects        of ADS contracts to support       request with the indication of the grounds
      may be “left out”.            other ADS-C connections       resolution of problems.           having active ADS-C contracts with the
                                    to accommodate this                                             aircraft. Then the ground may coordinate
                                    priority.                                                       with those grounds the termination of
                                                                                                    their ADS-C Contract. Or the ground may
                                                                                                    request the pilot to terminate the ADS-C
                                                                                                    Contract. In some aircraft types the pilot
                                                                                                    may have the capability to shut-down
                                                                                                    ADS-C contract for each ground
                                                                                                    independently and in others the pilot will
                                                                                                    have only the choice to shut down all
                                                                                                    active contracts.
                                                                                                    SC214/WG78 does not recommend to
                                                                                                    change ADS-C, the current definition
                                                                                                    satisfying the need.

STC   No message to advise flight   Create CPDLC message                                            This proposal for new messages is still
      when/where to make a          elements, such as:                                              under consideration by SC214/WG78.
      request again, in order to    UNABLE, REQUEST
      avoid using an “expect”       AGAIN AFTER [time]                                              Further coordination with NAT is
      message which is subject to   UNABLE, REQUEST                                                 required to assess the operational need for
      various interpretations       AGAIN AFTER PASSING                                             such proposed message
                                     UNABLE, REQUEST                                           Some “Expect” messages have been
                                     AGAIN AFTER                                               reworded such as the following:
                                     REACHING [level]                                                 UM7 EXPECT HIGHER AT [time]
                                     REQUEST HIGHER                                                   UM8 EXPECT HIGHER AT [Position]
                                                                                                      UM9 EXPECT LOWER AT [time]
                                     LEVEL AFTER [time]
                                                                                                      UM 10 EXPECT LOWER AT [Position]
                                     REQUEST HIGHER
                                                                                               These existing UMs are redundant with
                                     LEVEL AFTER PASSING
                                                                                               some of the proposed messages.
                                     REQUEST HIGHER
                                     LEVEL AFTER
                                     REACHING [level]
                                     REQUEST LOWER
                                     LEVEL AFTER [time]
                                     REQUEST LOWER
                                     LEVEL AFTER PASSING
                                     REQUEST LOWER
                                     LEVEL AFTER
                                     REACHING [level]
STC   Message elements used for      Re-write the text and        Suggest using the material   SC214/WG78 CPLDC Message Set has
      conditional clearances are     explanations                 prepared by NAT ATMG/35      been reviewed and updated according to
      frequently misunderstood                                                                 NAT ATMG/35 material. When required,
                                                                                               Message Element text and Message Intent
                                                                                               has been reworded to avoid confusion in
                                                                                               the execution of the instruction and to
                                                                                               ensure consistency between Message
                                                                                               Element and Intent.

STC   It is impossible to provide    Create message elements to                                SC214/WG78 CPLDC Message Set
      more than one frequency in a   enable providing                                          supports two messages to be used for the
      message                        secondary/back up                                         provision of secondary frequency.
                                                                                               UM238 SECONDARY FREQUENCY
                                                                                                           UM296 MONITOR SECONDARY
                                                                                                           FREQUENCY [unit id][frequency]

                                                                                                           UM238 message is concatenated to
                                                                                                           "CONTACT" or "MONITOR" messages

STC    RADIO is not one of the           Update the necessary                                              RADIO is one option of the Unit ID /
       ATSU options, so it is            message elements to add                                           Facility function parameter used
       impossible to instruct an         “RADIO” as an ATSU type                                           notably in CONTACT/MONITOR
       aircraft to contact or monitor,
       for example, Gander Radio

VG     There is no health checking       A system health check,         By continuously measuring the      This is FANS/ACARS network Issue.
       of the FANS connection.           similar to a ping, would be    response time to the pings, we     The SC214/WG78 SPR/INTEROP
       Sometimes a CPDLC                 periodically done by the       can determine the reliability of   Standards are ATN Compliant which
       connection will stop working      automation to ensure that      the connection                     provides a sort of “keep alive” function.
       for a particular aircraft (not    the connection is live. It                                        The user is notified of any disruption in
       all) and messages will not be     would also be used to                                             the CPLDC Connection.
       able to be sent or received.      measure latency time and
       After a period of time, the       help to determine the
       connection will come back         viability of the FANS
       and message could then be         connection.
       sent or received.

IATA   " CLIMB TO REACH                  In order to avoid confusion                                       SC214/WG78 Concurs.
       (flight level) BY                 we suggest another wording
       (position/time) ". The            of the clearance intent such                                      Each CPLDC Message Element and
       official intent of this           as "Adapt flight to reach                                         Intent is under review/assessment and,
       clearance, according to           and maintain specified FL                                         when required, is updated to avoid such
       ICAO DOC 4444 is :                before specified                                                  confusion in the execution of the
       "instruction that a climb is to   position/time" .                                                  instruction.
       commence at a rate such that
       the specified level is reached                                                                      SC214/WG78 will take in consideration
       at or before the specified                                                                          the proposed change of intent for each
       position/time". The common                                                                      message falling in this issue.
       understanding of this
       instruction is that pilots have                                                                 For the given example, each message
       to arrange their flight to                                                                      element containing “ BY [time]” or “BY
       reach specified FL before                                                                       [Position] “ have been replaced by
       specified position (this                                                                        message containing respectively “AT OR
       meaning was confirmed by                                                                        BEFORE [time] or AT OR BEFORE
       Shanwick ATC). When pilots                                                                      [Position]. Message intent has been
       are already at optimum FL                                                                       updated consequently but has to be
       and receive such an                                                                             reconsidered according to this proposal.
       instruction, they often delay
       the beginning of climb to
       reach the specified FL just
       before the specified
       position/time, which is in
       accordance with the
       instruction's meaning.
       Nevertheless, a synonym of
       "to commence" is "to begin"
       and some crews understand
       the clearance as in instruction
       to climb right after
       clearance reception

       Message elements used for         Re-define the message     This material was prepared by       SC214/WG78 has review and improved
       conditional clearances are        element text as follows   NAT ATMG (NAT ATMG/35               these CPLDC Messages. When required,
       frequently misunderstood          (insertions in grey       Summary of Discussions,             Wording and Intent are updated to avoid
                                         highlight, deletions in   paragraph 6.10 refers):             confusion in the execution of the
                                         strikeout)                With regard to the proposed         instruction. SC214/WG78 agreed on the
ATMG                                     UM21 AT OR AFTER          change to UM21, it is noted         following new wording:
                                         [time] CLIMB TO AND       that this is different from the
                                         MAINTAIN [altitude]       currently defined intent of         UM21 AT OR AFTER [time] CLIMB TO
                                                                   UM21 which is “An                   [level]
                                         UM24 AT OR AFTER
                                                                   instruction that at the specified   UM22 AFTER PASSING [position]
                                         [time] DESCEND TO
                                                                   time, a climb to the specified      CLIMB TO [level]
                                         AND MAINTAIN
                                      [altitude]                   level is to commence and once      UM24 AT OR AFTER [time] DESCEND
                                      UM22 AT AFTER                reached the specified level is     TO [level]
                                      PASSING [position]           to be maintained”. The NAT         UM25 AFTER PASSING [position]
                                      CLIMB TO AND                 ATMG agreed that this              DESCEND TO [level]
                                      MAINTAIN [altitude]          particular operational intent      UM26 CLIMB TO REACH [level] AT
                                      UM25 AT AFTER                was not required, and that the     OR BEFORE [time]
                                      PASSING [position]           use of such an instruction was     UM27 CLIMB TO REACH [level] AT
                                      DESCEND TO AND               intended to convey that the        OR BEFORE [position]
                                      MAINTAIN [altitude]          climb was to commence at or        UM28 DESCEND TO REACH [level]
                                                                   after the specified time. This     AT OR BEFORE [time]
                                      UM26 CLIMB TO
                                                                   applies equally to UM24.           UM29 DESCEND TO REACH [level]
                                      REACH [altitude] BY AT
                                                                   When this NAT ATMG                 AT OR BEFORE [position]
                                      OR BEFORE [time]
                                                                   suggestion was originally
                                      UM28 DESCEND TO
                                                                   reviewed by the NAT IMG
                                      REACH [altitude] BY AT
                                                                   working structure, it was not
                                      OR BEFORE [time]
                                                                   supported on the basis that it
                                      UM27 CLIMB TO                was not technically or
                                      REACH [altitude] BY          financially feasible to consider
                                      BEFORE PASSING               amending the current FANS
                                      [position]                   1/A message set; the intent of
                                      UM29 DESCEND TO              the suggestion was supported.
                                      REACH [altitude] BY
                                      BEFORE PASSING
       Current control authority is   Establish a mechanism to     It is possible that ADS-C          This issue is still under discussion in
       sometimes unable to            ensure that when an ADS-C    contracts are being retained       SC214/WG78.
       establish ADS-C connection,    contract is no longer        longer than required. Needs to     As defined in SC214/WG78 Standard,
       because other entities have    needed it is ended and the   be assessed how to                 when all ADS-C slots are allocated to
       “used up” all available        connection with the ATSU     prevent/minimize this.             grounds, ADS-C shall reject a new
ATMG   connections.                   is terminated.                                                  request with the indication of the grounds
                                                                                                      having active ADS-C contracts with the
                                                                                                      aircraft. Then the ground may coordinate
                                                                                                      with those grounds the termination of
                                                                                                      their ADS-C Contract. Or the ground may
                                                                                                      request the pilot to terminate the ADS-C
                                                                                                        Contract. In some aircraft types the pilot
                                                                                                        may have the capability to shut-down
                                                                                                        ADS-C contract for each ground
                                                                                                        independently and in others the pilot will
                                                                                                        have only the choice to shut down all
                                                                                                        active contracts.
                                                                                                        SC214/WG78 does not recommend
                                                                                                        changing ADS-C, the current definition
                                                                                                        satisfying the need.

       In order to apply “5 minutes      Create new message                                             SC214/WG78 created a new message to
       climb through” (PANS-ATM          element:                                                       support the expressed operational need. c), it is necessary   LEAVE [altitude] NO
       to apply a restriction that       LATER THAN [time]                                              UM265 LEAVE [level] AT OR BEFORE
       aircraft leave an altitude no                                                                    [time]
       later than a time.
                                                                                                        Intent: Instruction that the specified level
                                                                                                        has to be left at or before the specified

       “EXPECT” messages are             Re-write the message          Appropriate message elements     SC214/WG78 took special care of
       frequently misunderstood as       elements to use less          are required to respond to       EXPECT Messages.
       authorization to proceed in       suggestive wording, such as   “WHEN CAN WE EXPECT”
       accordance with the               ANTICIPATE, POSSIBLE          requests.                        Assessment of each EXPECT Message
       expectation                       or POSSIBLY                   A specific flight level should   has been performed with operational
                                                                       never be mentioned in            people and the current message set
                                                                       responses.                       reflects the result of the discussion.
                                                                                                        Some EXPECT messages have been
                                                                                                        removed due to a risk of
                                                                                                        misunderstanding and because no
                                                                                                        operational need has been confirmed.

                                                                                                        Some EXPECT messages have been
                                                                                                        deemed operationally required and when
necessary a new wording has been
proposed to avoid misleading.

UM/DM Paring consistency has also been
assessed to improved consistency.

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