Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to various transport category airplanes equipped with certain Mode C air traffic control (ATC) transponders manufactured by Rockwell Collins, Inc. This proposal would require testing each transponder; replacing certain parts in any transponder which fails the initial test and performing additional test(s); and making repairs, as necessary so that the transponder passes the test. This proposal is prompted by reports that indicate that the equipment used to conduct earlier tests of certain transponders did not detect certain malfunctions. An airplane equipped with such malfunctioning transponders could transmit inaccurate data concerning its altitude to a nearby airplane equipped with the traffic alert and collision avoidance system (TCAS II), causing the TCAS II to issue an erroneous resolution advisory to the pilot. The actions specified by the proposed AD are intended to prevent transmission of inaccurate data concerning altitude from one airplane to another, which could cause the pilot receiving the data to change course, either ascending or descending, and possibly lead to a mid-air collision or near mid-air collision.