Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 747 series airplanes. This proposal would require inspections, tests, and certain modifications of the thrust reverser control and indication system and wiring on each engine, and corrective action, if necessary. This proposal also would require installation of a terminating modification, and repetitive functional tests of that installation to detect discrepancies, and repair, if necessary. This proposal is prompted by the results of a safety review, which revealed that in- flight deployment of a thrust reverser could result in significant reduction in airplane controllability. 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, which could result in inadvertent deployment of a thrust reverser during flight, and consequent reduced controllability of the airplane.