Airworthiness Directives; Boeing Model 737-300, -400, and -500 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 737-300, -400, and -500 series airplanes, that requires interchanging the location of the hydraulic fuse and the flow limiter of the standby hydraulic system of the leading edge. This amendment also requires replacing the existing hydraulic fuses in the standby hydraulic system with new fuses. This amendment 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 in extreme cold environment, can adversely affect the operation of the fuse. The actions specified by this AD are intended to prevent such adversely affected operation of the fuse, which could result in the loss of all standby hydraulic system pressure and consequent severely reduced controllability of the airplane during certain flight phases.