Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 737 and 747 series airplanes. This proposal would require replacement of Waterman hydraulic fuse assemblies with modified assemblies. This proposal is prompted by reports of failure of hydraulic system A and the standby system due to corrosion on the magnesium piston of the hydraulic fuse and consequent failure of the fuse to close sufficiently to prevent the loss of hydraulic fluid from the system. The actions specified by the proposed AD are intended to prevent such failure of the fuse, which could result in the failure of one or more hydraulic systems and resultant reduced controllability of the airplane.