COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 747 Series Aeroplanes AD/B747/109 Passenger Oxygen System Continuous Flow Control Unit 5/92 Applicability: Boeing 747 series aircraft listed in Boeing Service Bulletin 747-35-2074 Revision 1. Requirement: Action in accordance with the Accomplishment Instructions of Boeing Service Bulletin 747-35-2074 Revision 1. Note: FAA AD 92-04-03 Amdt 39-8172 refers. Compliance: Within 4000 hours time in service after 30 April 1992. Background: The FAA has received reports of flow control units not activating at the proper altitude during a maintenance check of the system; the malfunction being caused by manufacturing defects in the flow control units. The defective units, if not replaced, can prevent the automatic deployment of oxygen to the passenger oxygen system in the event of loss of cabin pressure.