Performance of Category IllB Automatic Landings Using C/A Code Tracking Differential GPS

Stephen V. Rowson, Glenn R. Courtney, Richard M. Hueschen

Abstract:	An experimental DGPS precision approach and landing system was installed and flight tested on the NASA Langley Transport Systems Research Vehicle (TSRV), a Boeing 737-100. The GPS ground station and avionics units used Novatel lo-channel, narrow correlator, C/A code tracking receiver engines. Differential corrections generated in the ground equipment were adjusted using a carrier phase smoothing algorithm prior to being transmitted once every two seconds to the aircraft via a 2400 baud VHF data link. The GPS avionics converted DGPS position to vertical and horizontal angular deviations from the desired flight path. These deviations drove the aircraft flight control system in a manner emulating an instrument landing system (ILS) receiver. The GPS avionics did not make use of kinematic carrier phase tracking with on-the-fly cycle ambiguity resolution techniques, and was not enhanced with input from other systems such as barometric altimeter, radar altimeter, terrain mapping or inertial reference unit (IRU). However, the TSRV autoland flight control system included a radar altimeter (used for vertical flare guidance below 42 ft) and IRU (implemented to filter the “bends” in the glide path sometimes seen with ILS). A total of 40 DGPS-guided approaches and landings were performed at the NASA Wallops Flight Facility, 31 of them hands-off, automatic landings. Aircraft position was measured using a laser tracker. Total system error met the proposed Category III Required Navigation Performance (RNP) or “tunnel concept” accuracy requirements by a 300 percent margin laterally and 35 percent vertically. Touchdown dispersion for the 31 automatic landings also met Category III RNP requirements by approximately a 3-to-1 margin laterally and 2-to-1 longitudinally.
Published in:	Proceedings of the 1994 National Technical Meeting of The Institute of Navigation January 24 - 26, 1994 Catamaran Resort Hotel San Diego, CA
Pages:	759 - 767
Cite this article:	Rowson, Stephen V., Courtney, Glenn R., Hueschen, Richard M., "Performance of Category IllB Automatic Landings Using C/A Code Tracking Differential GPS," Proceedings of the 1994 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1994, pp. 759-767.
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