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					                                                                    AMCP WGW/WP5


       AERONAUTICAL MOBILE COMMUNICATIONS PANEL (AMCP)


                             Working Group of the Whole
                                 Montreal, Canada
                                  21-24 May 2002




      Liaison statement from AMCP WGC to OPLINKP
                     and related reply

                              Presented by the Secretary


This paper reproduces the following documents with minor editorial adjustments:

Attachment 1: Liaison statement from AMCP WGC/2 to OPLINKP (May 2001)
Attachment 2: Response from OPLINKP (April 2002)
                                                                    AMCP WGW/WP5


                         ATTACHMENT 1 TO WGW/WP5

          Liaison statement from AMCP WGC/2 to OPLINKP (May 2001)


AMCP (WGC) is currently conducting a comparative assessment of ADS-B links.
Background information is provided at Appendix A. In its assessment, AMCP is making
use of information gathered by the joint FAA/Eurocontrol ADS-B Technical Link
Assessment Team.
AMCP would like to request OPLINKP WGA to review the assumptions used by the
TLAT with regard to ADS-B operational requirements and report to AMCP on the extent
to which the assumptions are consistent with the ICAO ADS-B operational requirements
currently under the development by OPLINKP. It would be much appreciated if
OPLINKP WGA could report back to AMCP (ideally in time for the next meeting of
WGC, to be held from 15 to 19 October 2001). The assumptions used by TLAT are at
Appendix B, which reproduces Appendix G of the TLAT report. The full report is
available at the following websites:
www.eurocontrol.be/projects/eatchip/ads
www.faa.gov/safeflight21/

It should be noted that the link evaluation criteria used by the TLAT and reproduced in
Appendix B are not exclusively ADS-B related. OPLINKP is requested to concentrate its
review on ADS-B related requirements.

AMCP understands that the development of ICAO operational requirements has not been
completed yet. However, it should be noted that the assumptions are not intended to
replace the ICAO operational requirements, but only to be used to provide a
representative benchmark for the comparative performance analysis of ADS-B links.
Hence, OPLINKP is not requested to provide a detailed statement of consistency, but
only a general indication as to whether the assumptions could be considered broadly
representative of the expected ADS-B operational environment.




Appendix A    Background information    [not included]
Appendix B    Appendix G of TLAT Report [not included]
                                                                              AMCP WGW/WP5


                            ATTACHMENT 2 TO WGW/WP5

                                   Response from OPLINKP

(Extract from the summary of discussions and conclusions of the April 2002 meeting of
OPLINKP Working Group A)



[…]
Agenda Item 2: Review of assumptions used by the joint FAA/EUROCONTROL
ADS-B Technical Link Assessment Team (TLAT) with regard to ADS-B operational
requirements

7.1            WP/2 presented a request received from the Secretary of AMCP for the
OPLINKP to review assumptions used by the joint FAA/EUROCONTROL ADS-B Technical
Link Assessment Team (TLAT). AMCP (WG-C) was currently conducting a comparative
assessment of ADS-B links and was making use of information gathered by TLAT.

7.1.1            The request from AMCP noted that assumptions used in the TLAT Report were
not intended to replace the ICAO operational requirements, “but only to be used to provide a
representative benchmark for the comparative performance analysis of ADS-B links”.
Consequently, OPLINKP was not requested to provide a detailed statement of consistency, but
only a general indication as to whether the assumptions could be considered broadly
representative of the expected ADS-B operational environment.

7.1.2            It was recalled by the meeting that following ADSP/4 (1996), the panel had been
tasked with the development of an operational concept and operational requirements for the use
of a system to increase aircraft situational awareness and provide airborne separation assurance. It
was recognized even at ADSP/5 that because of the early stage of projects and trials, it would
have been premature to present operational requirements or an operational concept. Too many
issues remained, and still remain, unresolved to have provided the detail necessary for such a
document to be of any value. Consequently, the progress of the working group concentrated on
the progress of States, the potential for ADS-B to satisfy identified requirements, as well as a
detailed breakdown of the issues outstanding before such an application could be implemented.
Work had also commenced on an ADS-B concept of use.

7.1.3            Whilst it was recognized that the Standards and Recommended Practices
(SARPs) developed to date were technical in nature, actual implementation of any technical
means would need to satisfy the operational and functional requirements of the ATM applications
that they were intended to support. VDL Mode 4 and Mode S extended squitter SARPs were
capable of being adapted to meet changing requirements and to support new applications using
ADS-B. However, a technical means could not be considered finalized until research, technical
development, verification and validation had been completed. In this context, work by ICAO on
the completion of both technical and operational requirements, in the light of intended ATM
applications, should avoid progressing applications that exceed the possibilities really offered.

7.1.4         It was in this light that the meeting focussed its attention on the source
documents that the link evaluation criteria were based on. These included the Joint
Government/Industry Plan for Free Flight Operational Enhancements (August 1998, RTCA Free
                                                                              AMCP WGW/WP5

Flight Select Committee) and the RTCA DO-242, Minimum Aviation System Performance
Standards (MASPS) for ADS-B. Additional technical criteria were also developed. Consequently,
the meeting agreed that a determination needed to be made as to the appropriateness and maturity
of the applications/scenarios contained in these source documents and used as a basis for setting
the criteria to be evaluated. In this context, it was noted that, at the time of writing, DO-242 was
in the process of being revised as a new document DO-242A. To what extent would this
amendment change the basis for setting the criteria? Why was DO-242 being changed? Will the
system requirements at the MASPS level in the revision be based on operational ranges or on
particular applications? Are operational requirements still being determined in light of experience
(e.g. evolving requirements)? Do the source documents take into account lower traffic densities
and those States who have no interest at this time in the enhanced aspects of the application, and
are proposing limited services with benefits in the short to medium term?

7.1.5            While the guidance on performance criteria contained in the Manual of Air
Traffic Services Data Link Applications (Doc 9694) has not been fully taken into account, this
may not necessarily be a negative, noting that these performance figures considered a contract-
based ADS rather than a broadcast mode. Nevertheless, the working group was unsure as to the
extent the performance of such components as ground networks and human performance were
taken into account. Also, it was unclear to what extent an assumption had been made that the
integrity, continuity and availability would be the same for all applications. In this context, the
view was expressed that more emphasis should have been placed on those requirements
associated with advanced — surface movement guidance and control systems (A-SMGCS). It is
likely that these requirements, in certain scenarios, would be much more rigorous than for other
applications.

7.1.6              The view was also expressed that some ASAS operations may require a point to
point connection offering safe and reliable data link communications capability directly between
aircraft that is independent of a ground infrastructure. An example of such an operation might be
flight path deconfliction where an exchange of messages between the aircraft involved will be
required in order to negotiate the revised flight paths. This air-to-air data link would be
characterized by a capability to support time critical exchanges of messages and a safe, secure
and predictable behaviour, including authentication mechanisms. He noted that this need had not
been included in the assumptions used in TLAT.

7.1.7            The working group concluded its discussion on the subject, agreeing that the
assumptions could be considered broadly representative of the expected ADS-B operational
environment, but only to the extent that they applied to the source applications used in the
evaluation. It was also hoped that the questions put to the AMCP above would provide a suitable
check list for items to be considered in their on-going work. It was noted however, that
assumptions made, would not replace international acceptance of the intended ATM applications.

[. . . .]

				
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