COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 107 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Auxiliary Power Units AD/APU/9 PW901A APU Idler Gear and Cooling Fan Shaft 10/93 Applicability: Pratt and Whitney Canada PW901A Auxiliary Power Units (APU) installed in, but not limited to, Boeing 747-400 series aircraft. Requirement: Action in accordance with the requirements of Pratt and Whitney Canada Alert Service Bulletin Number A16159 Rev. 1. Note: Transport Canada Airworthiness Directive CF-93-09 and FAA Airworthiness Directive T93-10-51 refer. Compliance: Effective 16 September 1993: At the first main base transit check with an aircraft layover time exceeding 3 hours. Background: This Directive has been issued to address a possible smoke in cabin situation. The requirement follows advice of two incidents in which, fracture of the PW901A APU idler gear and cooling fan shaft, resulted in debris flooding the load gearbox allowing oil to enter the load compressor air system.