{"id":"F2006B03134","name":"AD/B747/236 - Honeywell Inertial Reference Units","slug":"ad-b747-236-honeywell-inertial-reference-units","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42506,"registerId":"commonwealth-F2006B03134-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"AIRWORTHINESS DIRECTIVE","sectionType":"part","heading":"AIRWORTHINESS DIRECTIVE","content":"# AIRWORTHINESS DIRECTIVE\n\n![](image.002.png)\n\n![](image.002.png)  \nFor 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.","sortOrder":0},{"sectionNumber":"AD/B747/236 Honeywell Inertial Reference","sectionType":"part","heading":"AD/B747/236 Honeywell Inertial Reference Units 12/2000","content":"# AD/B747/236 Honeywell Inertial Reference Units 12/2000\n\nApplicability: Model 747-400 series aeroplanes with line numbers 696 through 1187 inclusive equipped with Honeywell inertial reference units (IRU).\n\nRequirement: 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.\n\nRemoval 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.\n\n2. IRUs having Boeing Part Number S242T101-110, S242T101-111 or S242T101- 112 may not be installed on any Boeing 747-400 series aeroplane.\n\nNote: FAA AD 2000-20-20 Amdt 39-11932 refers.\n\nCompliance: For Requirement 1 \\- Before 30 May 2002.\n\nFor Requirement 2 \\- As of the effective date of this Directive.\n\nThis Airworthiness Directive becomes effective on 30 November 2000.\n\nBackground: 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.\n\nThis Directive requires removal of existing IRUs and installation of modified IRUs. These actions are intended to prevent loss of multiple IRUs in flight.\n\n![Signature of Eugene Paul Holzapfel, Delegate of the Civil Aviation Safety Authority.](image.003.png)  \n\nEugene Paul Holzapfel\n\nDelegate of the Civil Aviation Safety Authority 20 October 2000\n\n![](image.002.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 1 November 2000.","sortOrder":1}],"analysis":{"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The AD implements a focused corrective action for a specific safety problem (failure of multiple IRUs) by mandating replacement with modified units and forbidding certain part numbers. It does not broaden regulatory reach beyond that stated safety purpose, add unrelated obligations, or expand applicability beyond the specified 747-400 line numbers. The directive accepts compliance performed under a prior Boeing ASB, but that is an accommodation rather than an expansion of scope."},"complexity_factors":["Short document (two clear Requirements plus Applicability, Compliance, Background)","Single narrow applicability: Boeing 747-400 with line numbers 696–1187 equipped with Honeywell IRUs","Two substantive, non-nested obligations (replace units; ban specific part numbers)","One compliance deadline and one immediate prohibition (simple timing rules)","Cross-reference to Boeing Alert Service Bulletin (two revision dates mentioned) and FAA AD (informational only)","No large interpretation section, few defined terms, and no layered exceptions or conditional logic"],"plain_english_summary":"**What this instrument does (mechanically)\n\n- Requires operators of certain Boeing 747-400 aeroplanes to remove the existing Honeywell inertial reference units (IRUs) and install modified IRUs. (Requirement 1)\n- Prohibits installing IRUs with Boeing part numbers S242T101-110, S242T101-111 or S242T101-112 on those aeroplanes. (Requirement 2)\n- Sets deadlines: the replacement must be done before 30 May 2002; the prohibition on those part numbers is effective immediately from the AD's effective date (30 November 2000). (Compliance)\n- Accepts earlier removal/replacement done under Boeing Alert Service Bulletin (ASB) 747-34A2638 dated 29 January 1999 as compliant with Requirement 1. (Requirement 1)\n- The AD references an FAA airworthiness directive for related background. (Note)\n\nWho is affected\n\n- Owners and operators of Boeing 747-400 series aeroplanes with line numbers 696 through 1187 inclusive that are equipped with Honeywell IRUs. (Applicability)\n- Maintenance organisations and parts suppliers who install, supply or certify IRUs for those aircraft.\n\nWhy the AD exists (stated purpose) and how it works in practice\n\n- The AD says Boeing reported an incident in which the left and centre IRUs failed on a single flight; losing multiple IRUs can cause loss of navigation data. The AD requires replacement with modified units to reduce the risk of multiple IRU failures in flight. (Background; Requirement 1)\n\nPractical effects, costs and decision points (analyst notes)\n\n- Who pays: aircraft operators bear the direct costs — purchase of modified IRUs, labour for removal and installation, and aircraft downtime while the work is done. (Requirement 1; Compliance)\n- Supplier and procurement effects: the prohibition on specific Boeing part numbers (S242T101-110/111/112) limits the parts that can be fitted; operators must source the approved modified units. That changes procurement choices and may raise short-term parts costs or create supplier concentration if only certain suppliers can supply the modified units. (Requirement 2)\n- Operational disruption: each affected aeroplane must be taken to maintenance for the change, creating scheduling and opportunity costs (lost flying hours). The AD gives a compliance deadline (before 30 May 2002) which concentrates those scheduling demands. (Compliance)\n- Compliance pathways: the AD explicitly accepts earlier work done to Boeing ASB 747-34A2638 dated 29 January 1999 as meeting Requirement 1, so operators who already complied under that ASB do not need to repeat the work. (Requirement 1)\n- Enforcement and discretion: the AD is issued by the CASA delegate under CAR 1998 subregulation 39.1(1); it is a mandatory direction requiring specific maintenance actions. Any alternative methods of compliance would typically require approval from the regulator (not stated in the AD text). (Preamble; issuance)\n- Safety benefit vs cost: the stated safety benefit is prevention of simultaneous loss of multiple IRUs (navigation capability). That benefit is widely diffuse (passenger and public safety) while the costs are concentrated on the aircraft owners/operators and maintenance suppliers. (Background)\n- Implementation risks: potential shortfalls include availability of sufficient modified IRUs, lead times for parts, and maintenance capacity to perform installations before the deadline; those factors could increase commercial pressure on operators and service providers. (Requirement 1; Compliance)\n\nReferences within the AD\n\n- Requirement 1 (remove and install modified IRUs; acceptance of earlier ASB 29 Jan 1999)\n- Requirement 2 (prohibition of specific Boeing part numbers)\n- Compliance (deadlines: before 30 May 2002 for Requirement 1; immediate effect for Requirement 2)\n- Background (reason for AD: reported dual IRU failure on a single flight)\n\nBottom line (concise):\n\nThis AD compels identified 747-400 operators to replace existing Honeywell IRUs with modified units by a set date and forbids reinstalling certain Boeing part-numbered IRUs. The regulator's stated aim is to prevent loss of multiple IRUs in flight. The measure imposes acquisition and maintenance costs and scheduling burdens on operators while restricting which parts may be used for compliance."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope. It addresses a specific safety defect in specific aircraft (Boeing 747-400s, line numbers 696-1187) with specific equipment (Honeywell IRUs). The document has not expanded beyond its original purpose of mandating hardware replacement to prevent dual IRU failure."},"complexity_factors":["Very short document (under 400 words)","Only 2 substantive requirements with clear deadlines","Single applicability criterion (specific aircraft line numbers plus equipment type)","Minimal defined terms (only 'IRU' is abbreviated, and it's explained)","No cross-references to other legislation beyond a single note about a related FAA directive","Simple conditional logic: 'if you already did X, you don't need to do X again'","Clear, single-layer compliance structure with no exceptions to exceptions"],"plain_english_summary":"CASA requires operators of Boeing 747-400 aircraft (line numbers 696–1187) fitted with Honeywell IRUs to replace faulty navigation computers after Boeing reported simultaneous dual-IRU failures that can compromise position data, especially over water. \n\nBy 30 May 2002 airlines must install upgraded IRUs per Boeing’s repair instructions, and from 30 Nov 2000 three specific IRU part numbers are banned from installation; earlier compliance under Boeing’s 29 Jan 1999 bulletin is accepted."},"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"}},"importantCases":[],"_links":{"self":"/api/acts/ad-b747-236-honeywell-inertial-reference-units","history":"/api/acts/ad-b747-236-honeywell-inertial-reference-units/history","analysis":"/api/acts/ad-b747-236-honeywell-inertial-reference-units/analysis","conflicts":"/api/acts/ad-b747-236-honeywell-inertial-reference-units/conflicts","importantCases":"/api/acts/ad-b747-236-honeywell-inertial-reference-units/important-cases","documents":"/api/acts/ad-b747-236-honeywell-inertial-reference-units/documents"}}