Results of a Test Program For the Use of Differential GPS For Approach Guidance

Nico van Driel, Robert Krijn

Abstract:	In the context of the International Test Program for the Navstar Global Positioning System (GPS). managed by the GPS Joint Program Office of the US Department of Defense, the National Aerospace Laboratory NLR in The Netherlands has conducted a test program with the GPS receiver 3A. The tests were aimed at the investigation of the suitability of differential P-code GPS for precision-type aircraft approaches. with the emphasis on the available position accuracy. Flight trials were conducted with NLR's Fairchild Metro II research aircraft equipped with the GPS high-dynamics receiver 3A. A second receiver 3A was located at a surveyed position at the airfield, broadcasting the differential GPS corrections via telemetry. In the aircraft the data of the GPS receiver were processed, together with the differential corrections, to produce ILS-like localiser and glide slope deviation signals. These signals were presented to the evaluation pilot on the Primary Flight Display of a programmable Electronic Flight Instrument System. The aircraft was equipped with a position reference system that produces post flight a three-dimensional aircraft trajectory with an accuracy of a few decimeters near the runway. The flight test program was conducted at Amsterdam Schiphol International Airport using different runways and approach directions. All approaches, approximately 90. were flown manually. Four evaluation pilots participated in the program. The mean horizontal position error of Differential GPS (DGPS), as measured over all approaches, is 1.7 m at the crossing of the runway threshold with a RMS error of 5.3 m. The mean altitude error is -10.2 m with a RMS error of 7.0 m. With the ILS as a reference over a longer range, the accuracy and stability of the lateral guidance information proved to be very good, but suffered for the glide slope guidance from the altitude error and resolution-induced "jumpiness".
Published in:	Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990) September 19 - 21, 1990 The Broadmoor Hotel Colorado Spring, CO
Pages:	621 - 629
Cite this article:	van Driel, Nico, Krijn, Robert, "Results of a Test Program For the Use of Differential GPS For Approach Guidance," Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990), Colorado Spring, CO, September 1990, pp. 621-629.
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