Summary
We are revising an earlier proposed airworthiness directive (AD) for certain Boeing Model 737-600, -700, -700C, -800 and -900 series airplanes. The original NPRM would have required sealing the fasteners on the front and rear spars inside the main fuel tank and on the lower panel of the center fuel tank, inspecting the wire bundle support installation in the equipment cooling system bays to identify the type of clamp installed and determine whether the Teflon sleeve is installed, and doing related corrective actions if necessary. We subsequently issued a supplemental NPRM to revise the compliance time for the corrective actions specified in the original NPRM. This action resulted from a design review of fuel tank systems. This second supplemental revises the original NPRM by clarifying the applicability of certain actions for certain airplanes. We are proposing this second supplemental NPRM to prevent arcing at certain fuel tank fasteners in the event of a lightning strike orfault current event, which, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane.