Airworthiness Directives; Boeing Model 747 Series Airplanes Equipped With Pratt & Whitney JT9D-70 Series Engines

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that requires inspections, tests, and certain modifications of the thrust reverser control and indication system and wiring on each engine, and corrective action, if necessary. This amendment also requires installation of a terminating modification, and repetitive functional tests of that installation to detect discrepancies, 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 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.