Flight Testing WAAS for Use in Closely Spaced Parallel Approaches

Sharon Houck, Andrew Barrows, Bradford Parkinson, Per Enge, J. David Powell

Abstract:	In good weather, San Francisco International Airport can support approximately 60 landings per hour on its two par-allel runways which are 750 ft apart; however, current navigation and surveillance systems lack the accuracy required for two aircraft to fly through clouds in such close proximity. During even fairly benign instrument meteoro-logical conditions, the airport degrades to a one-runway operation, the landing rate drops to 30 per hour, an air-borne traffic jam ensues, and many passengers become restless. (ILS) for this task is due to the angular nature of its radio beam, typically 3 to 6 deg wide. Farther away from the runway, the resolution of the aircraft's absolute position accuracy degrades; for landings on parallel runways, the two ILS approach beams will eventually overlap some-where on the approach. Special equipment and procedures can allow parallel instrument approaches to runways as lit-tle as 3400 ft apart; however, these solutions are expensive and are not applicable to airports such as San Francisco with 750 ft runway spacing. GPS positioning from the Wide Area Augmentation Sys-tem (WAAS) can be used to create straight instrument approach corridors that are free of the angular dependence ILS. These high-accuracy parallel approaches do not overlap and navigational separation is possible, even far from touchdown. A prototype WAAS-based avionics suite was built at Stanford University and flight tested at Mof-fett Federal Airfield in the fall of 1998 onboard a Beech-craft Queen Air. Pilots flew 27 approaches using the needle-based Course Deviation Indicator (CDI) as well as 3-D "tunnel-in-the-sky” display. Data was gathered on flight technical error (FTE), the pilot's guidance-following accuracy and navigation sensor error (NSE), the accuracy the WAAS-derived guidance. Pilots flew the WAAS-based corridor approaches with less deviation from center-line than that of the ILS approaches. Additional data shows that using a tunnel-in-the-sky display dramatically reduced FTE both horizontally and vertically. Finally, sta-tistical models were generated for both horizontal and ver-tical FTE that may be used in computational models of aircraft approach trajectories.
Published in:	Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999) September 14 - 17, 1999 Nashville, TN
Pages:	1787 - 1798
Cite this article:	Houck, Sharon, Barrows, Andrew, Parkinson, Bradford, Enge, Per, Powell, J. David, "Flight Testing WAAS for Use in Closely Spaced Parallel Approaches," Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999), Nashville, TN, September 1999, pp. 1787-1798.
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