Airworthiness Directives; Cessna Model 500, 501, 550, S550, 551, and 560 Airplanes

The FAA is adopting a new airworthiness directive (AD) for certain Cessna Model 500, 501, 550, S550, 551, and 560 airplanes. This AD requires 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. This AD also requires the subsequent removal of the AFM revision and placard. This AD results from a report of a chafed electrical wiring harness, which was arcing inside the fuel tank. We are issuing this AD to prevent potential fuel vapor ignition in a fuel tank, which could result in explosion and loss of the airplane.