ACAS II Bulletin - Issue 24

5 November 2018

Occasionally, reports are filed that suggest that TCAS II may not have performed as specified, including cases like:

  • no RA was triggered despite close proximity to the threat aircraft, 
  • an RA was triggered in the absence of credible threats,
  • the RA was inappropriate (e.g. towards rather than away from the threat),
  • unusual RA sequences, or
  • technical anomalies.

If it is found that TCAS II performed in such a way, investigations are typically carried out by aircraft operators, ATC authorities and, in particularly serious cases, by State investigation bodies. The purpose of these investigations is to find out what happened, establish whether TCAS II has performed as designed, look into all the contributing factors, and finally formulate recommendations in order to prevent similar events in the future.

In this issue

In this issue, we have described some real-life cases that have been reported and investigated. These investigations allow us to establish what really happened in these events.


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ACAS team

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