Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to all Boeing Model 747 series airplanes, that currently requires repetitive inspections to detect cracking of the forward and aft inner chords and the splice fitting of the forward inner chord of the station 2598 bulkhead, and repair, if necessary. This proposal would add repetitive inspections of an expanded inspection area, which would end the inspections specified in the existing AD. This proposal also would limit the applicability of the existing AD. This proposal is prompted by reports indicating fatigue cracking was found on airplanes that had accumulated fewer total flight cycles than the threshold specified in the existing AD. The actions specified by the proposed AD are intended to detect and correct fatigue cracking of the forward and aft inner chords, the frame support, and the splice fitting of the forward inner chord of the upper corner of the station 2598 bulkhead, which could result in reduced structural capability of the bulkhead and the inability of the structure to carry horizontal stabilizer flight loads.