Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 757-200, -200PF, and -300 series airplanes. This proposed AD would require inspecting for damage of the ground brackets, ground wires, and terminal lugs of the auxiliary power unit (APU) battery and the APU start transformer rectifier unit (TRU) as applicable; and corrective and related investigative actions. This proposed AD is prompted by reports indicating that, during inspections on two airplanes, the ground brackets for the APU battery were found damaged. We are proposing this AD to detect and correct a damaged electrical bonding surface of the APU battery and APU start TRU ground connections, which could cause overheating of the ground connections and lead to possible consequent ignition of the adjacent insulating blankets.