A general methodology has been developed for failure mitigation in satellite‐based navigation systems. This new approach is founded on the direct evaluation of integrity risk under the unified consideration of all single‐element failure hypotheses and the no‐failure hypothesis. It is applicable to fault‐tolerant estimation and integrity monitoring. In particular, the algorithm has been investigated for application as an airborne element of the Local Area Augmentation System (LAAS) integrity monitoring architecture. In this system, GPS ranging measurements from multiple ground‐based reference receivers are to be used to mitigate the effects of reference receiver failures. The multiple hypothesis algorithm has been evaluated through analysis and simulation and has been shown to provide the tightest realizable protection limits for LAAS. The operational performance of the new algorithm has been compared with that of the approach currently under consideration by RTCA Special Committee‐159. The performance of the multiple hypothesis algorithm has been demonstrated using experimental data collected during a series of LAAS prototype flight tests in a Beechcraft King Air.

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A Local Area Augmentation System (LAAS) architecture alternative has been developed to provide satellite‐based navigation for aircraft precision approach and landing. Differential code and carrier phase measurements from GPS satellites and ground‐based airport pseudolites (APLs), located at each end of the approach runway, are optimally processed at the aircraft to improve vertical performance. In an operational sense, this performance improvement would be realized as increased LAAS availability. In addition, a new integrity monitoring architecture is introduced to provide the tightest achievable protection limits with respect to LAAS reference receiver failures. To demonstrate that the notional LAAS architecture is realizable, a prototype system was implemented at Moffett Federal Airfield in California for flight testing on a National Aeronautics and Space Administration (NASA) Beechcraft King Air. In this paper, the ground and air components of the prototype architecture implementation are described. Experimental results from King Air flight trials performed in September 1997 show exceptional navigation performance with the APL architecture, including a 95 percent vertical navigation error of 0.74 m in real time.

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