Airworthiness Directives; Boeing Model 747 Series Airplanes

This amendment supersedes 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 amendment adds repetitive inspections of an expanded inspection area, which ends the inspections specified in the existing AD. This amendment also limits the applicability of the existing AD. This amendment is prompted by reports indicating that 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 this 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.