Non-intrusive testing of an aircraft installed instrument landing system based on DGNSS

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 direct system interconnection. The portable test system produces differential corrections, integrity checks and final approach segment path construction data for each of the pseudoranges transmitted in accordance with the agreed to protocol in a broadcast data link message. The test system is placed in close proximity to 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 an VHF antenna coupler 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 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