Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 747-400 series airplanes. This proposal would require repetitive inspections to detect improper installation and fatigue damage of the end cap of the forward engine mount, and replacement of the forward engine mount end cap assembly with an improved end cap assembly. Such replacement, when accomplished, would terminate the repetitive inspections. This proposal is prompted by a report of fatigue cracking of end cap bolts, caused by improper installation. Subsequent investigation revealed that properly installed end caps also are subject to early fatigue cracking. The actions specified by the proposed AD are intended to prevent failure of the end cap assembly, which could lead to separation of the engine from the airplane in the event of a primary thrust linkage failure.