Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes powered by Pratt & Whitney JT9D-7 series engines, that currently requires detailed visual inspections of the lugs on the bulkhead fitting of the rear engine mount, and corrective action, if necessary. The existing AD also specifies optional ultrasonic inspections, which, if accomplished, extend the repetitive interval for the required detailed visual inspections. This action would require accomplishment of the previously optional ultrasonic inspections and, for certain airplanes, rework of the bulkhead fitting of the rear engine mount. The actions specified by the proposed AD are intended to detect and correct bushing migration, corrosion, or cracking of the lugs on the bulkhead fitting of the rear engine mount, which could result in separation of the engine from the airplane. This action is intended to address the identified unsafe condition.