Description

This article is intended to give an overview of the occurrences where a TCAS RA has not been followed (correctly) by the flight crew. It describes the possible scenarios and the safety barriers used to prevent or mitigate the safety effects of such occurrences.

TCAS is one of the last safety barriers to protect from an accident, the ones after it being pilot visual response (with limited applicability in Instrument Meteorological Conditions (IMC)) and providence (i.e. luck). Therefore, ICAO documents state that all RAs should be followed unless the safety of the aircraft is at risk.

One of the most common reasons for not following a TCAS RA is the visual acquisition of (what is perceived to be) the conflicting traffic. It is worth noting, however, that the flight crew might not be fully aware of the overall picture in complex traffic situations and therefore visual acquisition is not a valid excuse for procedural non-compliance.