Airworthiness Directives; Boeing Model 777-200, -300, and -300ER Series Airplanes

We are adopting a new airworthiness directive (AD) for all Boeing Model 777-200, -300, and -300ER series airplanes. This AD requires a one-time inspection to determine the material of the forward and aft gray water drain masts. For airplanes having composite gray water drain masts, this AD also requires installation of a bonding jumper between a ground and the clamp on the tube of the forward and aft gray water composite drain masts. 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.