Airworthiness Directives; Boeing Model 757-200 and 757-300 Series Airplanes

We are adopting a new airworthiness directive (AD) for certain Boeing Model 757-200 and 757-300 series airplanes. This AD requires installing a bonding jumper between a ground and the clamp on the tube of the forward and aft gray water composite drain masts. For certain airplanes, this AD requires inspecting existing aft bonding jumper assemblies that might be too short, repair if necessary, and replacing the bonding jumper assembly with a new, longer bonding jumper assembly if necessary. This AD results 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. We are issuing this AD 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.