Summary
We propose to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 747-200B, 747-200F, 747-300, 747SP, 747-400, and 747-400F series airplanes equipped with Rolls-Royce RB211- 524 engines; and certain Model 767-300 series airplanes equipped with Rolls-Royce RB211-524 engines. This proposed AD was prompted by multiple reports of uncommanded thrust reverser unlock events. This proposed AD would require replacing certain relays and relay sockets, and doing wiring changes. For certain airplanes, this proposed AD would also require installing new relay panels, and removing and installing certain components. Additionally, this proposed AD would require, for certain airplanes, accomplishing concurrent actions, which include installing an additional locking system on the thrust reversers, installing an additional locking gearbox on each engine and modifying system wiring for in-flight fault indications of the thrust reverser system, and installing a second locking gearbox system on the thrust reversers. We are proposing this AD to prevent an uncommanded thrust reverser deployment during takeoff or in-flight resulting in decreased airplane control and performance, possible runway excursions, and failure to climb.