Summary
We propose to adopt a new airworthiness directive (AD) for the products listed above. This proposed AD would require inspecting to determine whether a third Halon fire extinguisher bottle is installed in the auxiliary power unit (APU) fragment impact zone, revising the limitations section of the airplane flight manual to add restrictions for APU usage for certain airplanes having a third fire extinguisher bottle, and removing the third fire extinguisher bottle from certain airplanes. This proposed AD was prompted by notification from the airplane manufacturer that the third fire extinguisher bottle is mounted in a small-fragment impact zone. We are proposing this AD to prevent penetration of the bottle by fragments released due to a failure of the APU rotor system. The bottle could rupture and cause substantial damage to primary airframe structure and primary flight controls.