COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 747 Series Aeroplanes AIRWORTHINESS DIRECTIVE For the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CAR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section. AD/B747/236 Honeywell Inertial Reference Units 12/2000 Applicability: Model 747-400 series aeroplanes with line numbers 696 through 1187 inclusive equipped with Honeywell inertial reference units (IRU). Requirement: 1. Remove the left, centre and right IRUs and install modified IRUs in accordance with Boeing Alert Service Bulletin (ASB) 747-34A2638 Revision 1 dated 8 April 1999. Removal and replacement of the IRUs previously carried out in accordance with ASB 747-34A2638 dated 29 January 1999 is an acceptable method of compliance for this Requirement. 2. IRUs having Boeing Part Number S242T101-110, S242T101-111 or S242T101- 112 may not be installed on any Boeing 747-400 series aeroplane. Note: FAA AD 2000-20-20 Amdt 39-11932 refers. Compliance: For Requirement 1 - Before 30 May 2002. For Requirement 2 - As of the effective date of this Directive. This Airworthiness Directive becomes effective on 30 November 2000. Background: Boeing received a report of the failure of the left and centre IRUs on a single flight. The failure of multiple IRUs could result in the loss of navigation data during flight which could compromise the ability of the flight crew to maintain the safe flight and landing of the aeroplane. This Directive requires removal of existing IRUs and installation of modified IRUs. These actions are intended to prevent loss of multiple IRUs in flight. Eugene Paul Holzapfel Delegate of the Civil Aviation Safety Authority 20 October 2000 The above AD is notified in the Commonwealth of Australia Gazette on 1 November 2000.