Airworthiness Directives; Boeing Model 707-100, -100B, -300, -300B (Including -320B Variant), -300C, and -E3A (Military) Series Airplanes; Model 720 and 720B Series Airplanes; Model 737-100, -200, -200C, -300, -400, and -500 Series Airplanes; and Model 747 Airplanes

The FAA is adopting a new airworthiness directive (AD) for certain Boeing transport category airplanes. This AD requires repetitive tests of the overwing fuel fill ports for certain wing tanks; an electrical bonding resistance test between the bulkhead fittings of the engine fuel feed tube and the front spar inside the fuel tank of the wings; other specified actions; and applicable corrective actions if necessary. This AD is prompted by our determination that this AD is necessary to reduce the potential for ignition sources inside fuel tanks. We are issuing this AD to prevent arcing or sparking at the interface between the bulkhead fittings of the engine fuel feed tube and the front spar inside the fuel tank of the wings and between the overwing fuel fill ports and the airplane structure during a lightning strike. Such arcing or sparking could provide a possible ignition source for the fuel vapor inside the fuel tank and cause consequent fuel tank explosions.