Airworthiness Directives; Boeing Model 737-100, -200, -300, -400, and -500 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 737-100, -200, -300, -400, and -500 series airplanes. For certain airplanes, this AD requires 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 AD requires replacement of the existing transient suppression diode with an improved diode. This AD also requires a functional test to verify proper installation of each diode, and corrective action, if necessary. This amendment 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 this 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.