Airworthiness Directives; Boeing Model 747 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes equipped with General Electric Model CF6-45 or -50 series engines, that requires repetitive inspections and tests of the thrust reverser control and indication system, and corrective actions, if necessary. This amendment also requires installation of a thrust reverser actuation system (TRAS) lock, repetitive functional tests of that installation, and repair, if necessary. Installation of the TRAS lock terminates the repetitive inspections and certain tests. This amendment is prompted by the results of a safety review, which revealed that in-flight deployment of a thrust reverser could result in a significant reduction in airplane controllability. The actions specified by this 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.