What is the frequency of RAs?
It is estimated, through various monitoring programmes and data obtained from operators, that an RA occurs every approximately 1000 flight hours on short and medium haul aircraft. The number increases to 3000 hours for long haul aircraft. The results of monitoring of core European airspace (conducted within the EUROCONTROL PASS project) showed that in the vast majority of encounters (80%) only one aircraft involved in the encounter received an RA. It us because the threat aircraft was not TCAS equipped or the threat’s TCAS was in TA-only mode, or the geometry of the conflict was such that the RA was not generated on the TCAS-equipped threat aircraft. An RA encounter was observed every 2160 flight hours. The most common observed RA was the Adjust Vertical Speed RA which amounted for 67% of all RA, followed by the Climb/Crossing Climb (13%) and Descend/Crossing Descend (9%).
