Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain Boeing Model 747-400 series airplanes, that currently requires repetitive tests of the cone brake of the central drive unit (CDU) of the thrust reversers, and corrective actions if necessary. This action would require installation of a thrust reverser actuation system (TRAS) lock and various related modifications and installations. Following installation of the TRAS lock, this action also would require repetitive functional tests of the TRAS lock, and corrective action if necessary. These actions are intended to prevent an inadvertent deployment of a thrust reverser during flight, which could result in loss of control of the airplane.