Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to Boeing Model 747 series airplanes equipped with General Electric CF6-45 and CF6-50 series engines. This proposal would require an inspection to detect chafing of the fuel line or incorrect clearance between the fuel line and pneumatic duct insulation blanket; a fuel leak check and strut drain test; corrective action if necessary; replacement of the outboard strut fuel line coupling O-rings and retaining rings with new parts; replacement of the pneumatic duct boot with a new part; and, for certain airplanes, installation of a flame arrestor and drain line entry screens. This action is necessary to prevent leaking fuel line couplings, chafed fuel lines, restricted or clogged strut drain lines, migrating fluids or vapors toward ignition sources, and flashback of external flame into the strut; these conditions could result in an uncontained engine strut fire. This action is intended toaddress the identified unsafe condition.