Summary
The FAA is revising an earlier proposed airworthiness directive (AD) for certain Boeing Model 767-200 and -300 series airplanes. For certain airplanes, the original NPRM would have required repetitive inspections for discrepancies of the tube assemblies and insulation of the metered fire extinguisher system and the bleed air duct couplings of the auxiliary power unit (APU) located in the aft cargo compartment; and corrective actions if necessary. For certain other airplanes, the original NPRM would have required a one-time inspection for sufficient clearance between the fire extinguishing tube and the APU bleed air duct in the aft cargo compartment, and modification if necessary. The original NPRM resulted from one report indicating that an operator found a hole in the discharge tube assembly for the metered fire extinguishing system; and another report indicating that an operator found chafing of the fire extinguishing tube against the APU duct that resulted in a crack in thetube. This action revises the original NPRM by expanding the applicability and adding an inspection for signs of chafing and to verify sufficient clearance between the fire extinguisher system and the bleed air duct couplings of the APU. We are proposing this supplemental NPRM to prevent fire extinguishing agent from leaking out of the tube assembly in the aft cargo compartment which, in the event of a fire in the aft cargo compartment, could result in an insufficient concentration of fire extinguishing agent, and consequent inability of the fire extinguishing system to suppress the fire.