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

The FAA is adopting a new airworthiness directive (AD) for certain Boeing Model 737-200, -300, and -400 series airplanes. This AD requires replacing the existing fueling float switch in the auxiliary fuel tank with a new, improved fueling float switch, installing a new liner system inside the float switch conduit, and performing related investigative and other specified actions. This AD results from reports of chafing of the direct-current-powered float switch wiring insulation in the center fuel tank. We are issuing this AD to prevent contamination of the fueling float switch of the auxiliary fuel tank by moisture or fuel, and chafing of the float switch wiring against the float switch conduit in the fuel tank, which could present an ignition source inside the fuel tank that could cause a fire or explosion.