Summary
The FAA is revising an earlier proposed airworthiness directive (AD) for certain Boeing Model 757-200 and 757-300 series airplanes. The original NPRM would have required installing a bonding jumper between a ground and the clamp on the tube of the forward and aft gray water composite drain masts. The original NPRM resulted from a report of charred insulation blankets and burned wires around the forward gray water composite drain mast found during an inspection of the forward cargo compartment on a Model 767-300F airplane. For certain airplanes, this action revises the original NPRM by adding a new inspection of existing aft bonding jumper assemblies that might be too short, repair if necessary, and replacement of the bonding jumper assembly with a new, longer bonding jumper assembly if necessary. We are proposing this supplemental NPRM to prevent a fire near a composite drain mast and possible disruption of the electrical power system due to a lightning strike on a composite drain mast, which could result in the loss of several functions essential for safe flight.