Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 777 airplanes. This proposed AD would require a one-time inspection of the first bonding jumper aft of the bulkhead fitting to detect damage or failure and to determine the mechanical integrity of its electrical bonding path, and repair if necessary; measuring the bonding resistance between the fitting for the fuel feed tube and the front spar in the left and right main fuel tanks, and repairing the bonding if necessary; and applying additional sealant to completely cover the bulkhead fittings inside the fuel tanks. This proposed AD results from fuel system reviews conducted by the manufacturer. We are proposing this AD to prevent arcing or sparking during a lightning strike at the interface between the bulkhead fittings of the engine fuel feed tube and the front spar inside the fuel tank. This arcing or sparking could provide a potential ignition source inside the fuel tank, which, in combination with flammable fuel vapors, could result in fuel tank explosions and consequent loss of the airplane.