Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 737-200, -300, and -400 series airplanes. This proposed AD would require 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 proposed AD is prompted by reports of chafing of the direct-current- powered float switch wiring insulation in the center fuel tank. We are proposing 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.