Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 737-100, - 200, -300, -400, and -500 series airplanes. For certain airplanes, this proposal would require installation of a transient suppression diode in the wiring circuit of the refueling valve-to-float switch of each fuel tank. For certain other airplanes, this proposal would require replacement of the existing transient suppression diode with an improved diode. This proposal also would require a functional test to verify proper installation of each diode, and corrective action, if necessary. This proposal is prompted by incidents of electrical fire during fueling of the airplane, due to a short circuit and overheating of a transient suppression diode. The actions specified by the proposed AD are intended to prevent such conditions, which could result in electrical arcing and ignition of fuel vapors at the refueling receptacle for the fuel tanks, and consequent fire during airplane fueling.