Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 777-200 series airplanes. This proposed AD would require installing a new washer between the lower wing surface and the jam nut of the sump drain valve assembly. This proposed AD results from fuel system reviews conducted by the manufacturer. We are proposing this AD to prevent energy from a lightning strike on the bushing for the sump drain valve from arcing to the inside of the center fuel tank wall, which could create an ignition source in the fuel tank and result in a fuel tank explosion.