{"id":"F2006B03522","name":"AD/BAe 146/75 - Removal of Altitude Limitation in Icing Conditions","slug":"ad-bae-146-75-removal-of-altitude-limitation-in-icing-conditions","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":43089,"registerId":"commonwealth-F2006B03522-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BAe 146/75 - Removal of Altitude Limitation in Icing Conditions","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nBritish Aerospace BAe 146 Series Aeroplanes\n\nAD/BAe 146/75 Removal of Altitude Limitation in Icing Conditions\n\n  \n11/99\n\nApplicability: British Aerospace BAe 146-100, \\-200 and \\-300 aircraft with AlliedSignal ALF502R series engines.\n\nRequirement: 1. For each engine installation, incorporate modifications to prevent uncommanded power reductions in icing conditions in accordance with British Aerospace Service Bulletin 71-72-30473A, Revision 1 dated 2 November 1998, Accomplishment Instructions, Paragraph 2.A.\n\nNote 1: AD/ALF/16 mandates engine specific modifications to improve the fan core inlet anti-icing capability.\n\nNote 2: CAA (UK) AD 004-02-94R1 and FAA AD 99-15-06 also refer.\n\n    2. For fully modified aircraft, remove the existing altitude limitation and N2 limitation placards in accordance with British Aerospace Service Bulletin 71-72- 30473A, Revision 1 dated 2 November 1998, Accomplishment Instructions, Paragraph 2.B, Item 1.\n\nFor the purpose of this AD, a “fully modified aircraft” is one that incorporates the anti-icing improvement modifications referenced in Requirement 1 on all four engines.\n\n    3. Ensure the respective aircraft flight manuals comply with the configuration specified in British Aerospace Service Bulletin 71-72-30473A, Revision 1 dated 2 November 1998, Accomplishment Instructions, Paragraph 2.B, Item 2.\n\nUpon compliance with Paragraph 2.B, Item 2, remove the following “green” page amendments, titled Maximum Operating Altitude from the respective aircraft flight manuals:\n\nAFM No. 3.7 \\- A/146-200/41 dated 8 August 1997\n\nAFM No. 3.10..- A/146-300/9 dated 26 June 1996\n\nAFM No. 3.12 \\- A/146-300/19 dated 26 June 1996\n\nAFM No. 3.13 \\- A/146-100/20 dated 26 June 1996\n\n    4. For each aircraft that has at least one unmodified engine fitted in any position, install altitude limitation and N2 limitation placards in accordance with British Aerospace Service Bulletin 11-137-30405A.\n\nUse of a locally manufactured altitude limitation placard denoting a more restrictive altitude limitation (ie. < 26,000’) satisfies the intent of this Requirement.\n\nFor the purpose of this airworthiness directive an “unmodified “ engine in one that does not incorporate AlliedSignal Service Bulletin ALF/LF 72-1020, Revision 2.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\nNote 3: Requirement 4 addresses the action previously mandated by AD/BAe 146/69 to identify aircraft subject to the altitude limitation when operating in icing conditions. AD/BAe/69 has been cancelled.\n\nNote 4: Requirement 4 also provides for installation of an unmodified engine on a fully modified aircraft. If such action occurs the altitude restrictions in icing conditions must be re-applied. Operators are responsible to ensure flight crews and maintenance personnel are made aware of this requirement according to the dictates of their respective internal procedures.\n\nCompliance: 1. Before installation of a modified engine or no later than 31 December 2003 whichever occurs first.\n\n    2. On any occasion a fully modified aircraft is to be operated with the altitude limitation in icing conditions removed, but no later than 31 December 2003.\n\n    3. Within 2 months after the effective date of this airworthiness directive or prior to operating a fully modified aircraft with the altitude limitation in icing conditions removed, whichever occurs first.\n\n    4. Whenever an aircraft is operated after the effective date of this airworthiness directive with an unmodified engine installed in any position.\n\nThis Airworthiness Directive becomes effective on 4 November 1999.\n\nBackground: ALF502 engines installed on BAe146 aircraft are prone to a phenomenon known as “rollback” which is an uncommanded power reduction condition and loss of thrust control in certain icing conditions. There have been instances where simultaneous rollback occurred on multiple engines on the same aircraft.\n\nAltitude restrictions have been successful as an interim means to prevent rollback events. The modifications mandated by this directive will restore the full certificated operating envelope of the aircraft.\n\nThis AD also identifies actions that are required if an unmodified engine is installed on an aircraft and removes CASA imposed altitude restrictions from the aircraft flight manual.","sortOrder":0}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original scope as a targeted safety intervention for a specific aircraft type and known engine defect. The document addresses the rollback phenomenon in icing conditions as originally intended, with provisions for both modified and unmodified engine configurations representing a complete regulatory solution rather than scope creep."},"complexity_factors":["Multiple cross-references to external technical documents (British Aerospace Service Bulletins 71-72-30473A and 11-137-30405A, AlliedSignal Service Bulletin ALF/LF 72-1020)","Conditional requirements based on aircraft modification status ('fully modified' vs partially modified)","Four distinct compliance deadlines with different triggering conditions","Specific technical definitions required ('fully modified aircraft', 'unmodified engine')","Reference to cancelled predecessor directive (AD/BAe 146/69) and related foreign directives (UK CAA AD 004-02-94R1, FAA AD 99-15-06)","Precise flight manual amendment references with document numbers and dates"],"plain_english_summary":"This AD requires British Aerospace BAe 146‑100/200/300 aircraft with AlliedSignal ALF502R engines to have specified engine modifications to prevent in‑flight power “rollback” in icing, per the manufacturer service bulletin. Aircraft with all four engines modified may resume flying at any certified altitude; those with any unmodified engines must retain placards limiting altitude and updated manuals. It addresses multi‑engine power loss in icing; compliance was due 31 December 2003."},"flash_summary":{"complexity_score":6,"scope_assessment":{"changed":true,"description":"This AD changes the operational scope compared with the earlier interim approach: it replaces a broad CASA-imposed altitude limitation with a conditional rule that removes the limitation only for aircraft that have all four engines modified per the specified Service Bulletin (Requirement 1–2; Background). It cancels the prior AD that identified restricted aircraft (Note 3) while retaining mandatory placards and restrictions whenever an unmodified engine (i.e. lacking AlliedSignal SB ALF/LF 72-1020 Rev 2) is fitted (Requirement 4; Note 1). Practically, operators pay for engine modifications or ongoing placarding/AFM management, and must decide whether to modify all engines or accept continuing altitude limitations and associated operational/administrative controls (Compliance; Note 4)."},"complexity_factors":["Technical modification requirement: Mandates engine anti-icing work per British Aerospace Service Bulletin 71-72-30473A Rev 1 (Requirement 1) — requires engineering work and parts procurement.","Configuration-dependent legal effect: 'Fully modified' defined as all four engines modified; legal rights to remove altitude/N2 limits hinge on this (Requirement 2).","Conditional placarding rules: If any engine is unmodified operators must install altitude and N2 limitation placards, with allowance for locally produced, more restrictive placards (Requirement 4).","Cross-references to other technical documents/ADs: Relies on AlliedSignal SB ALF/LF 72-1020 Rev 2 to define 'unmodified', and notes CAA (UK) and FAA ADs for context (Note 1, Note 2).","Multiple, staggered compliance deadlines and triggers: Different actions due 'before installation', 'on any occasion', 'within 2 months' or 'whenever' an unmodified engine is fitted (Compliance section).","Operational/administrative burden on operators: Requires AFM amendments/removals, crew and maintenance awareness duties when engines are swapped (Requirement 3; Note 4).","Regulatory interplay and historical change: Cancels earlier AD/BAe 146/69 identification requirement and replaces interim altitude restriction approach with a modification-based solution (Note 3; Background)."],"plain_english_summary":"This Airworthiness Directive requires BAe 146-100/200/300 aeroplanes with AlliedSignal ALF502R engines to receive specified anti-icing modifications, and allows removal of CASA-imposed altitude and N2 limitations once all four engines are modified. It affects aircraft operators and maintenance organisations who must install modifications, update flight manuals and placards, or keep restrictions when unmodified engines are fitted, because the changes restore the full certified operating envelope subject to configuration checks."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bae-146-75-removal-of-altitude-limitation-in-icing-conditions","history":"/api/acts/ad-bae-146-75-removal-of-altitude-limitation-in-icing-conditions/history","analysis":"/api/acts/ad-bae-146-75-removal-of-altitude-limitation-in-icing-conditions/analysis","conflicts":"/api/acts/ad-bae-146-75-removal-of-altitude-limitation-in-icing-conditions/conflicts","importantCases":"/api/acts/ad-bae-146-75-removal-of-altitude-limitation-in-icing-conditions/important-cases","documents":"/api/acts/ad-bae-146-75-removal-of-altitude-limitation-in-icing-conditions/documents"}}