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

The FAA is superseding an existing airworthiness directive (AD) that applies to all Model 737-100, -200, -200C, -300, -400, and - 500 series airplanes. The existing AD currently requires repetitive detailed inspections for damage of the electrical wire and sleeve that run to the fuel boost pump through a conduit in the fuel tank, and arcing damage of the conduit and signs of fuel leakage into the conduit; replacement of the sleeve with a new, smaller-diameter sleeve; and related investigative and corrective actions, as applicable. This new AD reduces the inspection threshold for certain airplanes. This AD results from a report of a fuel tank explosion on a Model 727-200F airplane on the ground, and a report of chafed wires and a damaged power cable sleeve of a fuel boost pump discovered during an inspection on a Model 737-300 airplane. (The fuel boost pump installation on certain Model 737 airplanes is almost identical to the installation on Model 727 airplanes.) We are issuing this AD to detect and correct chafing of the fuel boost pump electrical wiring and leakage of fuel into the conduit, and to prevent electrical arcing between the wiring and the surrounding conduit, which could result in arc-through of the conduit, and consequent fire or explosion of the fuel tank.