Collision Risk in extended 500 ft RVSM Airspace with geometric altimetry

Abstract

Aircraft in the en-route flight phase are assigned to flight levels, currently separated by 1,000 ft, and based on a barometric height. When switching to geometric altimetry (i.e., altitude determination based on Global Navigation Satellite System (GNSS) measurements), the accuracy increases without further degradation at higher altitude, as is the case for barometric altimetry. Therefore, it is investigated whether the vertical separation minima could be reduced to 500 ft while using geometric altimetry, which doubles the airspace capacity and allows aircraft to fly closer to their optimal altitude, resulting in fuel savings. This research outlines whether this RVSM2 concept is feasible from a technical vertical collision risk perspective. The results show that the Target Level of Safety (TLS) could theoretically be met by a small margin. However, before RVSM-2 could possibly be implemented, other challenges must be overcome, such as issues related to the Airborne Collision Avoidance System (ACAS), jamming and spoofing of GNSS signals, and GNSS liability issues.