Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Cessna Model 500, 550, S550, 560, 560XL, and 750 airplanes. This proposed AD would require installing identification sleeves on the wires for the positive and negative terminal studs of the engine and/or auxiliary power unit (APU) fire extinguishing bottles, as applicable, and re-connecting the wires to the correct terminal studs. This proposed AD results from a report of mis-wired fire extinguishing bottles. We are proposing this AD to ensure that the fire extinguishing bottles are activated in the event of an engine or APU fire, and that flammable fluids are not supplied during a fire, which could result in an unextinguished fire in the nacelle or APU.