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 repetitive inspections for damage or cracking of the aft pressure bulkhead, and repair, if necessary. This amendment continues to require certain repetitive inspections for damage or cracking of the aft pressure bulkhead, and repair, if necessary. This amendment removes certain repetitive inspections for cracking of the bulkhead web to Y-ring lap joint area but retains the initial inspection for cracking in that area. This amendment also adds a one- time inspection from the forward side of the bulkhead to detect fatigue cracking of the upper segment of the bulkhead web, and follow-on corrective actions, if necessary. This amendment is prompted by reports indicating that the inspections required by the existing AD may not detect cracking of the bulkhead web in a timely manner. The actions specified in this AD are intended to detect and correct fatigue cracking of the upper segment of the bulkhead web, which could result in rapid depressurization of the airplane, and consequent reduced controllability of the airplane.