Airworthiness Directives; Allied Signal Commercial Avionics Systems CAS-81 Traffic Alert and Collision Avoidance Systems (TCAS) as Installed In, But Not Limited To, Various Transport Category Airplanes

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.