CAT III Simulated Landing Performance for GLS and ILS Systems

Tim Murphy, Len Anderson, Matt Harris and Nancy Hien Tang

Abstract:	This paper discusses a study of CAT III approach and landing performance based on GNSS Ground Based Augmentation System (GBAS). The study extends previous results on application of a signal model for Performance Type 1 (PT1) GBAS to include Performance Type 3 (PT 3 i.e. CAT III) criteria for signal accuracy, continuity and integrity. The PT 3 GBAS model is used to simulate landing performance of several aircraft. This landing performance evaluation using the GBAS model is a further step in the development and validation of satellite based landing systems. Samples of aircraft landing performance from Monte Carlo simulations are presented in this paper to compare the expected Cat III performance of autoland using GLS and ILS. The standards and requirements for GBAS (and LAAS) to support CAT I operations are nearly finalized. The international community is now engaged in the development of requirements for GBAS to support Cat II and Cat III operations. Proposed requirements have been developed by RTCA and others. This paper presents a standard model, consistent with the current and proposed GPS satellite configurations, for evaluation of GBAS Landing System (GLS) performance based on the proposed requirements for PT 3 GBAS. To this end, a GLS Model developed jointly by Boeing, Naval Air Warfare Center Aircraft Division (NAWCAD) and the Federal Aviation Administration (FAA) [1, 2] is extended to include satellite/ground system requirements consistent with PT 3 ground stations and Cat II and Cat III landing conditions. Both the GLS Cat I and Cat III Models and an FAAapproved ILS model developed by Boeing were integrated into Boeing aircraft simulations for different airplane models. Monte Carlo simulation studies of autoland performance were conducted to compare the landing performance of GLS versus ILS. In this paper the GLS PT 1 and PT 3 models are briefly reviewed and the results of the autoland simulation studies conducted by Boeing are presented. The study shows that the lateral landing performance achieved using the GLS PT 1 and PT 3 models is better than the performance using an ILS with Facility Category II performance as defined in ICAO annex 10. The longitudinal landing performance with GLS is comparable to the longitudinal landing performance using ILS. In all cases the simulated touchdown performance meets the performance requirements specified by the FAA and JAA. It is believed this study will support the international community in the development of requirements for GBAS to support CAT III operations. Historically, models of navigation system errors (NSE) based on the requirements for the NAVAID have been used in the aircraft certification process in the context of Monte Carlo simulation trials. In addition to NSE, the simulations exercise the range of conditions an aircraft may see during service, including the variation of atmospheric effects (wind speed and direction, turbulence level, etc.), runway altitude, slope and surface condition, and aircraft configuration (weight, center of gravity location, flap settings, etc.). Samples of aircraft landing performance from Monte Carlo simulations are presented in this paper to compare the expected performance of autoland using GLS and ILS.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	1679 - 1688
Cite this article:	Murphy, Tim, Anderson, Len, Harris, Matt, Tang, Nancy Hien, "CAT III Simulated Landing Performance for GLS and ILS Systems," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 1679-1688.
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