COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 747 Series Aeroplanes AD/B747/87 Aural and Master Fire Warning Systems 3/91 Applicability: All model 747-400 series aeroplanes listed in the Requirement Document. Requirement: Action in accordance with the technical requirements of FAA AD 90-26-08. Note: Boeing Alert SB 747-26A2171 also refers. Compliance: As specified in the Requirement Document with an effective date of 21 March 1991. Background: Reports indicate that with certain Integrated Display System (IDS) software installed, the aural and master caution systems of the fire detection system are inoperative. This failure cannot be identified during normal system checks, and if not corrected, could result in the failure of the system to annunciate a fire in the APU, engines, wheel wells or cargo compartments.