This paper examines position, velocity, and time (PVT) continuity in the terminal area provided by a LAAS ground station meeting current precision landing requirements. One of the major contributors to continuity risk is the unexpected loss of a GPS satellite. The availability of PVT horizontal navigation for the worst case satellite subset is determined for a Horizontal Alert Limit (HAL) of 0.1, 0.2, 0.3, and 0.6 nm. The differential corrections are assumed to be based on a Ground Accuracy Designator C (GAD-C) compliant ground station using three reference receivers. The horizontal protection limit (HPL) for PVT is calculated as defined in the updates to the LAAS MOPS (DO-253) approved by RTCA SC-159. This assessment is done for nominal and pessimistic spatial decorrelation factors as well as historical and pessimistic constellation state probabilities. The analysis is performed for 13 major airports in the U.S. The purpose of this work is to determine the probability that HPL{sub}(PVT) exceeds the horizontal alert limit for the worst case subset and assess the continuity based on this. The availability of PVT is also compared to the precision approach availability and RAIM non-differential availability. One example is to determine the probability that PVT continuity is available given that precision approach is available based on the Bias Approach Monitor (BAM) check. The results show that sufficient redundancy is available to meet PVT continuity requirements in the terminal area.
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