Summary
We are revising an earlier proposed airworthiness directive (AD) for certain Model 777-200, -300, and -300ER series airplanes. The original NPRM would have required installing Teflon sleeving under the clamps of certain wire bundles routed along the fuel tank boundary structure, and cap sealing certain penetrating fasteners of the main and center fuel tanks. The original NPRM resulted from fuel system reviews conducted by the manufacturer. This action revises the original NPRM by adding airplanes and adding and removing certain requirements. We are proposing this supplemental NPRM to prevent electrical arcing on the fuel tank boundary structure or inside the fuel tanks, which could result in a fire or explosion.