Airworthiness Directives; Boeing Model 747 Series Airplanes

This amendment supersedes an existing airworthiness directive (AD) applicable to certain Boeing Model 747 series airplanes. That AD currently requires repetitive inspections and tests of the thrust reverser control and indication system on each engine, and corrective actions, if necessary; installation of a terminating modification; and repetitive operational checks of that installation, and repair, if necessary. This amendment 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 in 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. This action identifies certain repetitive operational checks that were inadvertently omitted from the existing AD, and revises certain procedures for accomplishment of the operational checks and certain follow-on corrective actions.