Flightline Test of Differential Global Navigation Satellite System (DGNSS) Instrument Approach System

John F. Michaels

Abstract:	This paper describes and analyzes a method of dynamically testing an aircraft installed DGNSS Instrument Approach System, while the aircraft is stationary on the airport ramp, without any direct system interconnection. The patent pending portable test system produces differential correction, integrity checks and final approach segment path construction data for each of the outputted pseudoranges which are transmitted in accordance with the agreed to protocol in a broadcast data link message. The test system is placed in close proximity of the aircraft bottom mounted VHF data link antenna. The test system contains a GPS receiver and a top mounted GPS antenna similar to that contained in the aircraft to be tested. Therefore both the aircraft and the test system process virtually the same satellite signals and pseudoranges. The test system has a VHF antenna coupler (hat) at the end of approximately 7 to 8 meters of cable that is placed over the aircraft bottom mounted VHF DGPS data link antenna. The antenna coupler or hat inhibits the aircraft receipt of the DGPS/Local Area Augmentation System (LAAS) airport ground reference station differential correction data. The antenna coupler does provide a means for the test system to enter signals dynamically identical to a data link broadcast signal. This differentially corrected aircraft pseudorange data is used in conjunction with the test system constructed final approach segment path data and with the airborne navigation data base to supply navigation guidance signals to drive appropriate aircraft systems, such as displays, autopilots, and/or flight directors. Non-precision and precision approach capabilities can be tested and verified for CAT I, II, and III landings, including proper processing of data interrupts, warnings approach inhibits, alarm verification and/or any conditions that could effect a flight decision, in particular a loss of integrity.
Published in:	Proceedings of the 1998 National Technical Meeting of The Institute of Navigation January 21 - 23, 1998 Westin Long Beach Hotel Long Beach, CA
Pages:	773 - 778
Cite this article:	Michaels, John F., "Flightline Test of Differential Global Navigation Satellite System (DGNSS) Instrument Approach System," Proceedings of the 1998 National Technical Meeting of The Institute of Navigation, Long Beach, CA, January 1998, pp. 773-778.
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