GBAS GAST D availability analysis for business aircraft

This paper analyzes Initial GBAS GAST D availability at a set of current ILS CAT III airports. Eurocontrol Pegasus Availability Tool, designed for SESAR projects is used for the assessment. Overall availability of the GBAS GAST D system is considered, focusing on business aircraft specifics where applicable. Nominal as well as adverse scenarios are presented in order to determine whether GAST D can reach the required availability for business aircraft at CAT III airport locations and under which conditions. The availability target was set at 99.9% availability when considering satellite outages in a given constellation and 99.997% when no outages are included. Sensitivity simulations were run for different scenarios and impacts of geometry screening thresholds, scale heights, aircraft mask, ground mask, sigma pseudorange ground, sigma ionospheric gradient, simulated year and different approach point (decision height) were analyzed. Some were run for a limited set of ILS CAT III airports and most of them for an almost complete set of nominal airports. Business aircraft specific assumptions, as well as aircraft type independent parameters (constellations, satellite outages, etc.) are examined in the paper. Conclusion summarizes the overall outcome of the simulations, showing that Initial GBAS CAT II/III can provide sufficient availability for all or almost all ILS CAT III capable airports considered in this study; and under which conditions. Recommendations for parameters that can be influenced (e.g. antenna location) if necessary are provided. It can also be expected that the availability will increase with the increasing amount of GNSS satellites. The work shows how different parameters impact availability of initial GBAS GAST D service for business aircraft, and that sufficient availability of GAST D service can be expected at most airports.