Benefits of tightly coupled GPS/IRS for RNP operations in terrain challenged airports

RNP AR procedures are particularly beneficial for airports that are surrounded by high mountains. Unfortunately, such procedures using unaugmented GPS receivers are occasionally unavailable at low RNP values because the mountains mask low elevation satellites to the extent that GPS receivers are unable to provide adequate integrity for the procedure. This paper demonstrates how the honeywell IRS/GPS hybrid (HIGH) dramatically improves availability for low RNP AR operations at terrain challenged airports. The paper focuses on RNP AR approach/departure availability for four of the most terrain challenged airports currently using RNP AR operations: Linzhi, Tibet; Queenstown, New Zealand; Aspen, Colorado; and Quito, Ecuador. Analysis was performed via simulations that implement a high fidelity terrain database that provides masking information for all points along a trajectory. Data was studied for terrain masking under the nominal state of the current GPS almanac along with an impact analysis on availability when satellites become unavailable during planned/unplanned outages. Field test results are presented that corroborate the analysis. Both simulation and field test results show that the HIGH algorithm outperforms a GPS receiver under nominal conditions and is also significantly more robust to poor satellite geometry.