A Non-Intrusive Flightline Test of an Aircraft Installed DGNSS Instrument Landing System Integrity Function

John F. Michaels

Abstract:	A method has been evolved that gives the pilot and crew the ability to verifj that the installed DGNSS system can properly process data interrupts, warnings, approach inhibits, data within and outside protection levels and alert limits, alarm verification andlor any condition that could effect a flight decisionj in particular loss of integrity. The flightline tester is located within 30 meters of the aircraft. The tester contains a VHF Data Broadcast (VDB) receiver and transmitter, whose performance is similar to that used by the aircraft and the LAAS Ground Reference Station respectively. It will receive the reference station VDB (Message Type 1-8) as it processes the satellite data and outputs differential corrections and other pertinent information. The tester will receive, detect and process this data, adding on varying differential correction for each satellite in view to simulate aircrafl motion and output new dynamic VDB (Message Type 1-8) to the aircraft. Because the LAAS ground reference station has muhipath limiting antennas and is located at an airport site to further reduce multipath efkcts on the received da@ the use of its VDB for the processing of correction data will be as good as the reference station expected performance. For those airports that do not contain a LAAS ground reference statiom the tester will contain a GPS receiver capable of processing all satellites in view. Although its expected that muhipath will contribute additional unwanted errors, the tester processing of dynamic pseudorange corrections and the outputting of data within and outside protection levels and alert limits described above, will be able to test aircraft systems integrity, availability and continuity while stationary on the ramp, without any direct system interconnection. This paper will describe the need for simple non-intrusive gohm-go ramp testing to veri@ installed equipment petiormance and operational integrity. INTRODUCTION Landing an aircraft, under any weather conditions, presents another set of requirements and expectadons from the navigation systemj which comes down to, signal in space (S1S) accura~, continuity, availability and especially signal integrity. RTC~ ICAO, along with the FAA and industry are defining a system capable of meeting these landing system requirements. As stated by the FAA [1], “GPS, as designed, developed and deployed by the DoD will not totally satis& all civil aviation requirements for navigation and landing. For use in civil aviation, augmentations will be required to improve GPS accuracy for precision approaches, provide integrity and continuity for all phases of flight, and provide availability necessary to meet primary means of radio navigation requirements.” The Local Area Augmentation System (LAM) is being designed to meet the more stringent CAT IIAII requirements that exist. Beyond CAT III, the LAAS will provide the user with an all weather Surface Navigation capability. “The LAAS will provide the above requirements at a significant improvement in seMce flexibility, safety, and user operating cost, without the investment inexpensive facilities.” “The LAAS will be used for CAT I, II and III approaches, including CAT IIIb which requires navigational system guidance through rollout. Other likely or potential applications of the LAAS include the following: depmture, high speed tumdfs, missed approach, vertical takeoff and landing operations, flare initiation over uneven terrain, and general terminal area navigation.” RTCA Special Committee SC-159 Working Group WG-4A has outputted the following document in final draft form: l Minimum Aviation System Performance Standards (MASPS) For The Local Area Augmentation System (LAAS) RTCA Paper No. 037-98/SC159-778. [2] l GNSS Based Precision Approach Local Area Augmentation System (LAAS) Signal-in-Space Interfhce Control Document (ICD) RTCA Paper No. 038-98/SC159-779. [3] These are scheduled for completion in mid 1998. In addition, the following document is scheduled for completion end 1998 or early 1999: l The LAAS Minimum Operation Performance Standards (MOPS) A test of the installed system needs to be performed on the ramp/flightline after initial installation as part of the certification process, to verify a mew report, after a maintenance action on the radar, prior to equipment removal for repair, and to give the flight crew the necessary degree of confidence that the equipment can perform its intended fimctions. The test is performed to insure crew members that the system can process data interrupts, alerts and warnings, satellite health status, approach inhibits, alarm verification and/or any condition that could effect a flight decision, in particular, loss of integrity. A ramp test can ver@ installed equipment performance and operatioml integrity. This non-intrusive tester concept, to be described, will make use of COTS (commercially off-the-shelf) equipment that meets the required system performance objectives detailed in the MASPS and MOPS. The tester acts as a dynamic ground refenime station simulator broadcasting the VDB data on a designated frequency different from that used by the airport LAAS ground reference station.
Published in:	Proceedings of the 54th Annual Meeting of The Institute of Navigation (1998) June 1 - 3, 1998 The Adams Mark Hotel Denver, CO
Pages:	675 - 688
Cite this article:	Michaels, John F., "A Non-Intrusive Flightline Test of an Aircraft Installed DGNSS Instrument Landing System Integrity Function," Proceedings of the 54th Annual Meeting of The Institute of Navigation (1998), Denver, CO, June 1998, pp. 675-688.
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