Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 737-300, - 400, and -500 series airplanes. This proposal would require interchanging the location of the hydraulic fuse and the flow limiter of the standby hydraulic system of the leading edge. The proposed AD also would require replacing the existing hydraulic fuses in the standby hydraulic system with new fuses. This proposal is prompted by reports of a performance test of the hydraulic fuses, which revealed that the positioning of the flow limiter in the existing configuration, and excessive fusing volumes of some of the fuses, can adversely affect the operation of the fuse. The actions specified by the proposed AD are intended to prevent such adversely affected operation of the fuse, which could result in the loss of all hydraulic system pressure and consequent severely reduced controllability of the airplane.