Summary
This document revises an earlier proposed airworthiness directive (AD), applicable to certain Boeing Model 737, 757, and 767 series airplanes, that would have required repetitive inspections of certain motor operated hydraulic shutoff valves to detect malfunctioning; and replacement with new valves, if necessary. That proposal also would have required eventual replacement of certain existing valves with new valves, which would have constituted terminating action for the repetitive inspections. That proposal was prompted by reports that the motor switch contacts on certain hydraulic shutoff valves were misaligned, causing subsequent malfunction of those valves. This new action revises the proposed rule by extending a certain compliance time and revising certain actions. The actions specified by this new proposed AD are intended to prevent failure of the motor operated hydraulic shutoff valves, which could result in leakage of hydraulic fluid to the engine fire zone, reduced ability to retract the landing gear, loss of backup electrical power or other combinations of failures; and consequent reduced controllability of the airplane.