Summary
This document revises an earlier proposed airworthiness directive (AD), applicable to certain Boeing Model 747-400, -400D, and -400F series airplanes, that would have required modification of the P212 and P213 panels of the cabin pressure control system. That proposal was prompted by a report of in-flight loss of cabin pressurization control due to a single failure of the auxiliary power unit (APU) battery. This action revises the proposed rule by adding new requirements, for certain airplanes, to modify the P5, P6, and P7 panels, and the W4701, W4703, and W4908 wire bundles, as applicable. The actions specified by this proposed AD are intended to prevent loss of control of the cabin pressurization system, which could result in rapid depressurization of the airplane. Such rapid depressurization could result in deleterious physiological effects on the passengers and crew; and airplane diversions, which represent an increased risk to the airplane, passengers, and crew.