Summary
This document proposes to revise an existing airworthiness directive (AD), applicable to various transport category airplanes equipped with Allied Signal Commercial Avionics Systems CAS-81 TCAS. That AD currently requires a revision to the Airplane Flight Manual (AFM) to provide the flightcrew with procedures to cycle power to the TCAS processor via the circuit breaker or power bus, and to perform a TCAS functional test to verify proper operation of the TCAS. That action was prompted by reports of failure of the audio output of the CAS-81 TCAS. The actions specified by that AD are intended to ensure that the flightcrew is advised of the potential hazard associated with failure of the audio output of the CAS-81 TCAS, and of the procedures necessary to address it. This action would add a revision of the AFM requirements that would provide an alternative method of compliance with the currently required AFM revision; and would provide for a modification to the TCAS processor, which, if accomplished, terminates the requirements of the AD.