{"id":"F2006B03503","name":"AD/BAe 146/53 Amdt 3 - APU Bay Forward Firewall","slug":"ad-bae-146-53-amdt-3-apu-bay-forward-firewall","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":43057,"registerId":"commonwealth-F2006B03503-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BAe 146/53 Amdt 3 - APU Bay Forward Firewall","content":"![](image.001.png)\n\n![](image.001.png)  \nAIRWORTHINESS DIRECTIVE\n\nFor the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/BAe 146/53 Amdt 2 and issues the following 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.\n\n![](image.001.png)\n\nBritish Aerospace BAe 146 Series Aeroplanes\n\nAD/BAe 146/53\n\nAmdt 3\n\n  \nAPU Bay Forward Firewall 5/2002\n\nApplicability: All Series BAe 146 aircraft and all Avro 146-RJ aircraft, which have embodied Modification HCM36019A.\n\nRequirement: Action in accordance with BAE Systems Mandatory Service Bulletin 26-035 Revision 2.\n\nNote: UK CAA AD 007-05-95 refers.\n\nCompliance: Before 19 July 1995 for the initial inspection, and thereafter at intervals not to exceed 200 cycles until the embodiment of Modification Service Bulletin 26-035-36179A, or; every 500 cycles after embodiment of 26-36-36179B.\n\nThe compliance time for the initial inspection requirement remains unchanged by this issue.\n\nThis Airworthiness Directive becomes effective on 16 May 2002.\n\nBackground: Reports have been received of cracking on the forward face of the APU bay forward firewall bulkhead.\n\nAmendment 1 introduced Modification 26-36-36179B to the compliance requirements.\n\nAmendment 2 deleted reference to the Garrett APU installation in the applicability, as this Directive requires an inspection of the firewall regardless of APU type.\n\nAmendment 3 is issued in response to a revision of the Requirement document, which changes the compliance inspection interval of 400 cycles to 500 cycles.\n\nAmendment 2 of this Airworthiness Directive became effective on 23 May 1996 Amendment 1 of this Airworthiness Directive became effective on. 7 December 1995.\n\nBritish Aerospace BAe 146 Series Aeroplanes\n\nAD/BAe 146/53 Amdt 3 (Continued)\n\nThe original issue of this Airworthiness Directive became effective on 19 July 1995.\n\n![Signature of David Villiers, Delegate of the Civil Aviation Safety Authority.](image.002.png)  \n\nDavid Alan Villiers\n\nDelegate of the Civil Aviation Safety Authority 27 March 2002\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 24 April 2002.","sortOrder":0}],"analysis":{"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"},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"Amendment 3 does not expand the AD’s substantive scope; it modifies the technical compliance interval (changing the post‑modification inspection interval from 400 cycles to 500 cycles) and updates the Requirement document reference. Earlier amendments (Amdt 1 and Amdt 2) adjusted applicability language and introduced modification options, which altered operational detail, but this third amendment is a technical tuning of the inspection frequency rather than a broadening of the AD’s purpose (which remains to detect and correct cracking of the APU bay forward firewall)."},"complexity_factors":["Short directive (one-page AD text) with limited sections (Applicability, Requirement, Compliance, Background).","References to multiple external documents: BAE Systems Mandatory Service Bulletin 26-035 Revision 2, Modification Service Bulletins 26-36-36179A and 26-36-36179B, and UK CAA AD (increases compliance complexity).","Conditional compliance intervals depending on embodiment of specific modifications (200 cycles vs 500 cycles) — a simple conditional but materially important.","History of amendments (Amdt 1, 2, 3) with prior changes to applicability and intervals — requires reading amendment history to understand current obligations.","A somewhat anomalous preservation of an initial inspection deadline predating the AD’s effective date (requires attention to ensure operators understand continuing obligations)."],"plain_english_summary":"**What this instrument does (mechanics)**\n\n- This is an Airworthiness Directive (AD) that requires inspections and possible modification of the Auxiliary Power Unit (APU) bay forward firewall on certain BAe 146 / Avro 146-RJ aeroplanes. (See: Applicability; Requirement; Compliance.)\n- The AD revokes the earlier version (Amdt 2) and re-issues the directive under CASA’s regulatory power. The required work must be done “in accordance with BAE Systems Mandatory Service Bulletin 26-035 Revision 2.” (Requirement.)\n- The AD sets specific inspection timings: an initial inspection deadline (unchanged by this amendment), repeating inspections at intervals that depend on whether certain manufacturer modifications have been embodied. Until Modification Service Bulletin 26-36-36179A is embodied, repeat inspections must not exceed 200 cycles; after embodiment of 26-36-36179B the interval is every 500 cycles. (Compliance.)\n- The AD became effective 16 May 2002 and is linked to reports of cracking on the forward face of the APU bay firewall. (Background; signature and effective date.)\n\n**Who this affects**\n\n- Aircraft owners/operators and their maintenance organisations that operate BAe 146 series and Avro 146-RJ aeroplanes which have embodied Modification HCM36019A. (Applicability.)\n- Maintenance providers who carry out inspections and embodied modifications required by the BAE mandatory service bulletin.\n- Regulators and certifying personnel who must accept and record compliance with the AD.\n\n**Why it matters (stated safety issue and practical effect)**\n\n- The AD responds to reported cracking of the APU bay forward firewall bulkhead (Background). The mechanical effect is to force inspections and, where applicable, the introduction of a modification that changes ongoing inspection frequency.\n\n**Costs, incentives and trade-offs**\n\n- Who pays: aircraft operators bear the direct costs — inspection labour, possible repairs, parts, and aircraft downtime. Maintenance organisations bear execution costs and must maintain competence and documentation.\n- Incentives: the AD creates an economic choice for operators — either accept more frequent inspections (higher recurrent cost and scheduling burden) or invest to embody the indicated modification (up‑front cost but longer inspection intervals: 200-cycle intervals reduced to 500 cycles after embodiment of 26-36-36179B). (Compliance.)\n- Opportunity cost: downtime for inspections/modification displaces revenue‑producing flying time and may require reallocating aircraft or leasing replacements.\n- Implementation risk and compliance burden: inspections must follow the manufacturer’s mandatory service bulletin. That delegates method and technical detail to the OEM document, potentially requiring access to that document and possible approval for non‑standard methods. The AD cross-references specific service bulletin numbers and a UK CAA AD, which increases dependency on external documents for compliance.\n\n**Effects on private enterprise and competition**\n\n- Independent maintenance organisations can perform the work if they follow the mandatory service bulletin and regulatory approval processes; however, reliance on OEM service instructions can raise compliance costs (access to the document, possible proprietary parts or tooling) which may favour larger MROs or OEM-affiliated providers.\n- The modification pathway (embodying 26-36-36179B) reduces inspection frequency and therefore recurring maintenance cost, which may improve aircraft availability and lower lifecycle maintenance costs if the upfront modification cost is justified.\n\n**Concrete behaviour changes required**\n\n- Operators must schedule and complete the initial inspection by the stated deadline (the AD preserves the existing initial inspection deadline). Thereafter operators must perform periodic inspections at the intervals specified unless they embody the stated modification, in which case a longer inspection interval applies. (Compliance.)\n- Operators must follow BAE Systems Mandatory Service Bulletin 26-035 Revision 2 when undertaking the required actions. (Requirement.)\n\n**Notes on textual and procedural features**\n\n- The AD explicitly ties compliance mechanics to external documents (manufacturer service bulletins and a referenced UK CAA AD). That means the AD sets obligations but delegates the technical method to those documents. (Requirement; Note.)\n- This amendment (Amdt 3) changes the inspection interval in the requirement document from 400 cycles to 500 cycles; earlier amendments removed an APU‑type limitation and introduced the modification 26-36-36179B into the compliance regime. (Background.)"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"The legislation maintains its original scope — addressing cracking in the APU bay forward firewall on BAe 146 aircraft. Amendment 3 is a technical update that changes only the inspection interval (400 to 500 cycles) following a revision to the underlying manufacturer service bulletin. The core safety purpose and affected aircraft population remain unchanged from the original 1995 directive."},"complexity_factors":["Multiple amendment versions referenced (Amendments 1, 2, and 3) with different effective dates","Conditional compliance schedule: 200-cycle intervals before modification, 500-cycle intervals after modification","Cross-reference to external technical document (BAE Systems Mandatory Service Bulletin 26-035 Revision 2)","Cross-reference to UK CAA AD 007-05-95","Specific applicability criteria tied to aircraft modification status (HCM36019A)","Nested modification references (26-035-36179A vs 26-36-36179B) with different compliance outcomes"],"plain_english_summary":"This AD revokes Amendment 2 and issues Amendment 3 to AD/BAe 146/53, mandating inspections of the APU-bay forward firewall on BAe 146 and Avro 146‑RJ aircraft with modification HCM36019A. It responds to detected cracks in a fire‑containment structure, requires an initial inspection by 19 July 1995, and sets recurring checks (every 200 cycles until the mod, then every 500 cycles thereafter). It affects owners, operators and maintenance organisations and is effective 16 May 2002."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bae-146-53-amdt-3-apu-bay-forward-firewall","history":"/api/acts/ad-bae-146-53-amdt-3-apu-bay-forward-firewall/history","analysis":"/api/acts/ad-bae-146-53-amdt-3-apu-bay-forward-firewall/analysis","conflicts":"/api/acts/ad-bae-146-53-amdt-3-apu-bay-forward-firewall/conflicts","importantCases":"/api/acts/ad-bae-146-53-amdt-3-apu-bay-forward-firewall/important-cases","documents":"/api/acts/ad-bae-146-53-amdt-3-apu-bay-forward-firewall/documents"}}