Summary
This document proposes to adopt a new airworthiness directive (AD) that would apply to certain AlliedSignal Aerospace (AlliedSignal) KT 76A ATC transponders that are installed on aircraft. The proposed AD would require incorporating a modification on the affected transponders that consists of replacing two resistor network modules with glass- coated modules. The proposed AD is the result of reports of these ATC transponders transmitting misleading encoding altimeter information to ground-based ATC radar sites and nearby Traffic Alert and Collision Avoidance System (TCAS)-equipped aircraft. The actions specified by the proposed AD are intended to prevent the transmission of misleading encoding altimeter information between affected aircraft caused by the inability of these ATC transponders to coordinate with ground-based ATC radar sites and nearby TCAS-equipped aircraft.