Airworthiness Directives; Boeing Model 747 Series Airplanes

This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that currently requires ultrasonic inspection of certain engine strut diagonal brace lugs for cracks, and replacement, if necessary. This amendment requires new repetitive inspections to detect discrepancies of the diagonal brace lugs, and rework of the diagonal brace lug, if necessary. In lieu of accomplishing the rework for certain cases, this amendment provides for an option to defer the rework by accomplishing repetitive inspections and resealing the bushing. This amendment also provides for an optional terminating modification for repetitive inspections. This amendment is prompted by additional reports of fatigue cracking in the diagonal brace lug. The actions specified in this AD are intended to prevent such fatigue cracking, which could result in failure of the strut and consequent separation of the engine from the airplane.