GPS standard positioning service (SPS) aircraft en route RAIM availability for continental United States

The FAA is considering using GPS and GPS augmentations for civilian aircraft navigation. This paper investigates the capability of the existing GPS constellation to meet FAA RAIM (receiver autonomous integrity monitoring) requirements for en route civilian flights over the continental United States (CONUS). The analysis shows that the current GPS constellation does not meet the FAA en route requirements when the effect of expected satellite failures requiring replacements are considered. An enlarged constellation, with either 5 additional satellites in a 0°-inclination plane or 6 additional satellites distributed in the 55°-inclination planes, will achieve the (1-10 ^-5) RAIM availability requirement. The sensitivity of RAIM availability to various system parameters was also studied. These include: receiver masking elevation angle, horizontal navigation error limit, aiding baro-altimeter measurement error, and probability of missed detection. Reducing the allowable elevation angle to 0°, which may be permissible for en route flights, significantly improves availability provided by the current 24 satellite constellation from 0.9976 to 0.9905