COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 747 Series Aeroplanes AD/B747/98 Auxiliary Power Unit (APU) Pneumatic Ducts 11/91 Applicability: Boeing 747 series aeroplanes as listed in FAA Airworthiness Directive 91-15-24 Amdt 39-7089. Requirement: Action in accordance with the Technical Requirements of FAA AD 91-15-24. Note: Boeing Service Bulletin 747-36-2081 and 747-36-2092 refers. Compliance: Required prior to the accumulation of 7 000 flight cycles or within the next 3 000 flight cycles after the 14 November 1991, which ever occurs later. Background: FAA AD action prompted by reports of cracked or ruptured APU ducts that have caused damage to adjacent structure, pneumatic ducts, and hydraulic lines. This condition, if not corrected, could result in damage to the adjacent structure, pneumatic ducts, hydraulic lines and/or electrical wiring.