Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to all Boeing Model 747-400 series airplanes, that currently requires various inspections and functional tests to detect discrepancies of the thrust reverser control and indication system, and correction of any discrepancy found. This action would reduce the repetitive interval for one certain functional test. This proposal is prompted by reports indicating that several center drive units (CDU) were returned to the manufacturer of the CDU's because of low holding torque of the CDU cone brake. The actions specified by the proposed AD are intended to ensure the integrity of the fail safe features of the thrust reverser system by preventing possible failure modes in the thrust reverser control system that can result in inadvertent deployment of a thrust reverser during flight.