EASA SIB 2009-16: Misinterpretation of ACAS Resolution Advisory (RA) Aural Annunciation Messages

What to do

Flight crews should be trained and reminded to correctly interpret and respond to ACAS II RA aural messages, particularly the 'Adjust Vertical Speed, Adjust' advisory. Operators are encouraged to plan for and implement an upgrade to TCAS II version 7.1 when it becomes available. No mandatory compliance deadlines are specified in this bulletin.

Summary

EASA Safety Information Bulletin SIB No: 2009-16 addresses the misinterpretation of ACAS Resolution Advisory (RA) aural annunciation messages, particularly the 'Adjust Vertical Speed, Adjust' (AVSA) message. This bulletin applies to all turbine-powered aeroplanes equipped with ACAS II (TCAS II Version 7.0) that meet specific weight or passenger seating criteria, including commercial and non-commercial operations. The document highlights the importance of correct pilot responses to RA messages to maintain safe separation from other aircraft.

What changed

EASA SIB No: 2009-16 introduces clarifications on the correct interpretation of various ACAS II RA aural messages, emphasizing the required pilot actions for each type of RA. It also recommends operators consider upgrading to TCAS II version 7.1, which includes a new 'Level Off, Level Off' (LOLOL) aural warning to reduce misinterpretation risks. This bulletin provides guidance rather than mandatory regulatory changes.

Why it matters

Misinterpretation of ACAS II RA aural messages can lead to incorrect pilot responses, potentially causing loss of separation and serious incidents. Aviation professionals, including flight crews and operators, must understand the correct actions associated with each RA to ensure flight safety. Compliance teams and maintenance organizations should be aware of the benefits of upgrading to TCAS II version 7.1 to enhance safety and reduce pilot confusion.