GPS/IRS/FMS Integration for RNP Airspace Operations

Tom McDavid, Timothy Murphy, and George Sotolongo

Abstract:	This paper describes tbe approach taken to integrate GPS into an existing multisensor navigation system on a commercial jet transport. The goal has been to develop a certiBable system providing benefits to the airlines without imposing unreasonable constraints or training requirements on a scheduled operator. The accuracy, integrity, availability and continuity of function aspects of Required Navigation Performance (RNP) are discussed. Integrity is defined in terms of a containment surface. Availabiiity of navigation signals and navigation equipment are defmed as well as levels of totaI system availability. The Boeing Specitication GPS Sensor Unit (GPSSU) is described, followed by the mechanization of Receiver Autonomous Integrity Monitoring in the GPSSU. Accuracy and integrity levels are output by GPSSU qsing the ligure of merit (FOM) and horizontal integrity limit (HIL) labels. The general philosophy of multisensor navigation system integration witbin the Flight Management System (FMS) on the 747-400 is presented. The GPSSU interface with the FMS and other navigation/display/crew alerting avionics are shown in a functional block diagram. The FMS mechanization of RNP is described. An alternate integrity function has been implemented to provide integrity when GPS integrity monitoring cannot support the RNP. This allows use of GPS with its high accuracy during most RAIM outages and eliminates the need to frequently revert to less accurate means of navigation. Predictions of GPS/Inertial navigation and integrity availabiiity are presented. First, the various assumptions used in the analysis, such as constellation state are, discussed. RAIM availability and RAIM outage durations for a number of constellation states are shown. Additionally, predictions of RAIM continuity of function at a threshold of 0.3 NM are made. RAIM availability and outage durations are then combined to show the global availability of different levels of RNP for the integrated GPS/IRS/FMS system. Recently completed flight tests in Australia are described, followed by a discussion of various operational considerations.
Published in:	Proceedings of the 1995 National Technical Meeting of The Institute of Navigation January 18 - 20, 1995 Disneyland Hotel Anaheim, CA
Pages:	401 - 412
Cite this article:	McDavid, Tom, Murphy, Timothy, Sotolongo, George, "GPS/IRS/FMS Integration for RNP Airspace Operations," Proceedings of the 1995 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 1995, pp. 401-412.
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