Summary
The FAA is revising an earlier proposed airworthiness directive (AD) for certain Cessna Model 500, 501, 550, S550, 551, and 560 airplanes. The original NPRM would have required revising the airplane flight manual (AFM) to prohibit use of the wing fuel boost pumps for defueling under certain conditions; installing a placard; doing other specified investigative and corrective actions as necessary; and modifying the boost pumps. The original NPRM also would have required the subsequent removal of the AFM revision and placard. The original NPRM resulted from a report of a chafed electrical wiring harness, which was arcing inside the fuel tank. This action revises the original NPRM by identifying certain service information not identified in the original NPRM. We are proposing this supplemental NPRM to prevent potential fuel vapor ignition in a fuel tank, which could result in explosion and loss of the airplane.