Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747SP, 747-400, 747-400D, and 747-400F series airplanes. This proposed AD was prompted by a determination that a certain fastener type that penetrates the fuel tank walls has insufficient bond to the structure, and energy from a lightning strike or high-powered short circuit could cause arcing to occur at the ends of fasteners in the fuel tanks. This proposed AD would require, for certain airplanes, reconfiguring the clamps of certain wire bundles, applying sealant to certain fasteners that penetrate the fuel tank walls, installing cushion clamps and polytetrafluoroethylene (TFE) sleeves, inspecting to determine if sealant was applied to certain fasteners, and applying sealant if necessary. This proposed AD would also require, for all airplanes, revising the maintenance or inspection program, as applicable, to incorporate new, more restrictive airworthiness limitations. The FAA is proposing this AD to address the unsafe condition on these products.