US Patent 7599164 Lightning protection system for aircraft composite structure

A lightning-protected conductive composite fuel tank includes a conductive material arrayed on an outer surface to at least partially cover a fastener centerline. Through holes extend along the fastener centerline through the conductive material and the underlying fuel tank shell. These through holes are countersunk into the fuel tank shell to a depth such that a fastener in a through hole will avoid electrical continuity or communication with the conductive material on the fuel tank outer surface. The gap in the countersunk through holes, between the fastener heads and the coextensive outer surface of the fuel tank, is filled with a dielectric or nonconductive material.