What is a uisance RA?
ICAO Annex 10 states that an RA shall be considered a ‘nuisance’ unless, at some point in the encounter in the absence of ACAS, the horizontal separation and the vertical separation would have been simultaneously less than the following values: Above FL100: horizontal separation: 2.0 NM; vertical separation 750 ft Below FL100: horizontal separation: 1.2 NM; vertical separation 750 ft It needs to be noted that the evaluation whether the RA was ‘nuisance’ or ‘unnecessary’ can be done only in hindsight. In real-time the pilot has little chance to correctly evaluate the threat (e.g. assess whether the threat aircraft is levelling off at its cleared level).
