Summary
We propose to adopt a new airworthiness directive (AD) for certain Cessna Aircraft Company Model 500, 501, 550, 551, S550, 560, and 650 airplanes. This proposed AD was prompted by reports of smoke and/or fire in the tailcone caused by sparking due to excessive wear of the brushes in the air conditioning (A/C) motor. This proposed AD would require inspections to determine if certain A/C compressor motors are installed and to determine the accumulated hours on certain A/C compressor motor assemblies; and repetitive replacement of the brushes in the A/C compressor motor assembly, or, as an option to the brush replacement, deactivation of the A/C system and placard installation; and return of replaced brushes to Cessna. We are proposing this AD to prevent the brushes in the A/C motor from wearing down beyond their limits, which could result in the rivet in the brush contacting the commutator, causing sparks and consequent fire and/or smoke in the tailcone with no means to detect or extinguish the fire and/or smoke.