Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 747 SP, SR, - 100, -200, and -300 series airplanes. This proposal would require repetitive operational tests of the reversible gearbox pneumatic drive unit (PDU) or the reversing air motor PDU to ensure that the unit can restrain the thrust reverser sleeve, and correction of any discrepancy found. This proposal is prompted by the results of an investigation, which revealed that, in the event of thrust reverser deployment during high-speed climb or during cruise, these airplanes could experience control problems. 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 in the thrust reverser control system that can result in inadvertent deployment of a thrust reverser during flight.