AD FAA-2018-0276

We propose to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 747-100, -100B, -100B SUD, -200B, - 200C, -200F, -300, -400, -400D, 747SP, and 747SR, and 747-8 series airplanes. This proposed AD was prompted by reports indicating that additional areas of Boeing Material Specification (BMS) 8-39 flexible urethane foam were found during an inspection required by a related AD. This proposed AD would require inspecting for BMS 8-39 flexible urethane foam insulation in the floor panel assemblies and the power drive unit (PDU) cover assemblies; doing applicable on-condition actions; modifying certain dripshields; and replacing BMS 8-39 foam strips on certain dripshields with BMS 8-371 foam strips. We are proposing this AD to address the unsafe condition on these products.