AD FAA-2021-0258

The FAA proposes to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 747-400, 747-400D, and 747-400F series airplanes. This proposed AD was prompted by reports of burned Boeing Material Specification (BMS) 8-39 urethane foam found in certain locations on the airplane; investigation revealed that the fire- retardant properties degrade with age. This proposed AD would require inspecting the insulation blankets in certain areas of the forward cargo compartment for exposed BMS 8-39 urethane foam, not encapsulated by a protective fire resistant barrier, and for seal integrity, and replacing the BMS 8-39 urethane foam and seal if necessary. The FAA is proposing this AD to address the unsafe condition on these products.