Summary
This document proposes the supersedure of 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. That action also 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. That action also adds a one-time detailed visual 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 action would require that the one-time inspection be accomplished repetitively, and would add additional repetitive inspections. The actions specified by the proposed AD are intended to detect and correct fatigue cracking of the bulkhead web, which could result in rapid depressurization of the airplane, and consequent reduced controllability of the airplane.