Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Thales Avionics TA/RA VSI-TCAS indicators, installed on but not limited to certain transport category airplanes equipped with TCAS II change 7 computers (ACAS II). This proposal would require a revision to the Airplane Flight Manual (AFM) to advise the flightcrew to follow the audio annunciation when an RA fail message is triggered during a multi-aircraft encounter. This proposed AD would also require modification of the software for the TA/RA VSI-TCAS indicator, which would terminate the requirement for the AFM revision. This action is necessary to prevent the TA/RA VSI-TCAS indicator from displaying a conflicting "RA FAIL" message during a multi-aircraft encounter, which could result in the flightcrew ignoring the correct aural command and traffic display information if the flightcrew believes the TCAS II computer has malfunctioned, and consequently lead to a mid-air collision with other aircraft. This action is intended to address the identified unsafe condition.