Correlation Properties of GBAS Guidance Information

Andreas Lipp and Aline Lhermite

Abstract:	For aircraft precision approach and landing, the GBAS system will complement and replace current ILS systems. The interchangeable use of GBAS and ILS systems does not only depend on the technical equivalence, but also on the possibility of designing approach procedures useable for both systems. The ICAO criteria for procedure design (PANS-OPS) use for this purpose a mathematical model called the “Collision Risk Model” (CRM).The error distributions in the CRM were obtained from test flights using ILS and simulation extrapolations and need to be reviewed for the use of GBAS. Particularly the assumption of independence between horizontal and vertical errors, valid for ILS because of its technical design, has to be reviewed. The ICAO Obstacle Clearance Panel (OCP), charged with developing GBAS approach criteria has proposed to perform his validation by experimental means and test flights have been performed by three organisations. While results from pre-operational equipment have confirmed the assumption of independence, those with experimental equipment were initially inconclusive. The authors have developed a simulation model to assess the influence of differences in experiment design, noting especially the influence of the limited number of samples available from flight trials and the influence of proprietary filtering typically employed in commercially certified equipment. The model results show a high likelihood for a similar, low level of correlation for both GBAS and ILS, thus validating the assumptions for the CRM and allowing its use for development of GBAS PANS-OPS criteria based on an ILS equivalence methodology. It also demonstrates the influence of non-standardised, manufacturer proprietary filter designs on the aircraft performance and underscores the need for regular update and verification of the aircraft performance data in the CRM in order to be representative of the equipment in use.
Published in:	Proceedings of the 58th Annual Meeting of The Institute of Navigation and CIGTF 21st Guidance Test Symposium (2002) June 24 - 26, 2002 Hyatt Regency Hotel Albuquerque, NM
Pages:	279 - 290
Cite this article:	Lipp, Andreas, Lhermite, Aline, "Correlation Properties of GBAS Guidance Information," Proceedings of the 58th Annual Meeting of The Institute of Navigation and CIGTF 21st Guidance Test Symposium (2002), Albuquerque, NM, June 2002, pp. 279-290.
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