{"id":"F2006B02291","name":"AD/AL 250/81 - Third Stage Turbine Wheels","slug":"ad-al-250-81-third-stage-turbine-wheels","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41521,"registerId":"commonwealth-F2006B02291-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"AIRWORTHINESS DIRECTIVE","sectionType":"part","heading":"AIRWORTHINESS DIRECTIVE","content":"# ![](image.001.png)  \nAIRWORTHINESS DIRECTIVE\n\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.\n\n![](image.001.png)\n\nAllison Turbine Engines \\- 250 Series","sortOrder":0},{"sectionNumber":"AD/AL 250/81 Third Stage Turbine Wheels ","sectionType":"part","heading":"AD/AL 250/81 Third Stage Turbine Wheels 6/2002","content":"# AD/AL 250/81 Third Stage Turbine Wheels 6/2002\n\nApplicability: Allison 250 \\- C28 Engines with third stage turbine wheels Part Number (P/N) 6899383 and with Serial Numbers (S/N) listed in Table 1 of this Directive.\n\nRequirement: Remove from service all turbine wheels P/N 6899383 listed by S/N in Table 1 of this Directive.\n\nNote: FAA AD 2002-06-08 refers.\n\nCompliance: Effective 13 June 2002; as per Table 2 of this Directive.\n\nThis Airworthiness Directive becomes effective on 13 June 2002.\n\nBackground: Fractures of the third stage turbine blade tips and shrouds could cause uncommanded shutdowns. New lower life limits have been established to address this problem.\n\nThis Directive requires the removal from service of certain turbine wheels that exceed the new lower life limits.\n\nTable 1. S/N’s of Affected Third Stage Turbine Wheels\n\n| HX91428R | HX91489R | HX91707R |\n| -------- | -------- | -------- |\n| HX91456R | HX91490R | HX91708R |\n| HX91457R | HX91492R | HX91709R |\n| HX91428R | HX91489R | HX91707R |\n| HX91456R | HX91490R | HX91708R |\n| HX91457R | HX91492R | HX91709R |\n| HX91458R | HX91493R | HX91710R |\n| HX91459R | HX91494R | HX91711R |","sortOrder":1}],"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"},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The Directive remains narrowly focused on removing specific third‑stage turbine wheels that exceed newly established, lower life limits. It does not broaden regulatory reach beyond that safety‑driven purpose (no new inspection regimes, no additional equipment mandates, no expansion to other engine types). Any apparent change in scope in the supplied text reflects clerical issues (duplicate entries, missing Table 2) rather than an expansion of the Directive's substantive scope."},"complexity_factors":["Short, single‑issue instrument (remove listed parts)","One part number specified (P/N 6899383) and 15 unique serial numbers listed in Table 1","Table 1 contains duplicated rows in the supplied text (clerical ambiguity)","References an external FAA AD (FAA AD 2002‑06‑08) — external cross‑reference","References a Table 2 for compliance timing that is not included in the supplied text (missing element increases practical complexity)","No nested exceptions or multiple conditional paths — straightforward mandatory removal"],"plain_english_summary":"**What this directive does (mechanics)\n\n- Applies to: Allison 250‑C28 turbine engines that contain a third‑stage turbine wheel with part number P/N 6899383 and one of the serial numbers (S/N) listed in Table 1 of the Directive (Applicability).\n- Action required: Operators must remove from service any turbine wheel with P/N 6899383 that is listed by S/N in Table 1 (Requirement).\n- Timing: The Directive became effective on 13 June 2002 and sets compliance timing \"as per Table 2\" (Compliance). The Directive also notes a related FAA airworthiness directive (Note / FAA AD 2002‑06‑08).\n- Safety reason given: Fractures of third stage turbine blade tips and shrouds can cause uncommanded engine shutdowns; new, lower life limits have been adopted and this Directive removes from service wheels that exceed those limits (Background).\n\nWho this affects\n\n- Aircraft operators and owners that operate helicopters or aircraft with Allison 250‑C28 engines containing the affected wheels.\n- Maintenance organisations and certifying staff who must remove, replace and record the removed components.\n- Parts suppliers who may be asked to supply replacement third‑stage turbine wheels.\n\nWhy it matters (stated purpose and practical effects)\n\n- Purpose claimed: Prevent in‑service failures (blade tip/shroud fractures) that can lead to unexpected engine shutdowns by enforcing new, lower life limits (Background and Requirement).\n- Immediate mechanical effect: Specific parts identified by serial number must be taken out of service; affected engines will need replacement wheels or other corrective maintenance before return to service.\n\nCosts, incentives, trade‑offs and implementation issues\n\n- Who pays: The aircraft owner/operator bears the direct costs — replacement parts, engine removal/installation labour, and aircraft downtime.\n- Who decides/executes: The CASA delegate issued the AD; operators and their maintenance organisations decide scheduling and select replacement parts or repairs, and must certify the work.\n- Incentives and private‑sector effects: Demand for replacement third‑stage wheels will rise for affected operators; if a single supplier controls availability, prices or lead times could increase, affecting operational schedules.\n- Compliance burden: Removing engines/wheels is labour‑intensive and may require removing the engine from the airframe or grounding the aircraft until a replacement is fitted and certified.\n- Trade‑offs: The Directive reduces operational risk from blade/shroud fracture at the cost of parts, maintenance, and potential temporary loss of aircraft availability.\n- Implementation risk / ambiguity: The Directive references a Table 2 for compliance timing that is not included in the text supplied here; Table 1 as printed contains duplicated rows (possible clerical error). These issues can create uncertainty about exact compliance deadlines and which serial numbers are intended, increasing the risk that operators contact CASA or the manufacturer for clarification before acting.\n- Substitution and operational responses: Operators may track fleet life more closely, retire affected engines earlier, or source overhauled/repaired wheels; they might also reallocate aircraft to maintain schedules.\n\nOther practical notes\n\n- The AD cross‑references FAA AD 2002‑06‑08; operators commonly consult that AD and the manufacturer service information for implementation details and for locating replacement parts.\n- The Directive is narrow in scope by design: it targets specific part and serial numbers rather than imposing a fleet‑wide inspection regime.\n\n(References: Applicability; Requirement; Compliance; Background; Note / FAA AD.)"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This AD maintains its original narrow scope. It addresses a specific safety defect in a specific engine model's turbine wheels with identified serial numbers. There is no evidence of scope creep; the directive remains tightly focused on the original safety issue (fracture risk in third stage turbine wheels) and does not expand to cover other engine components, models, or operational scenarios."},"complexity_factors":["Very short document (approximately 300 words)","Only 3 operative sections: Applicability, Requirement, and Compliance","Single, unambiguous action required (removal from service)","Limited to specific part number (P/N 6899383) and enumerated serial numbers (12 unique S/Ns listed, though Table 1 contains duplicates)","No nested conditions, exceptions, or cross-references to other legislation (only a non-binding note referencing FAA AD 2002-06-08)","Clear, fixed compliance date with no alternative methods or conditional timelines","No defined terms section — common aviation terminology used without specialised legal definitions"],"plain_english_summary":"This CASA Airworthiness Directive mandates immediate removal from service of specific third‑stage turbine wheels (P/N 6899383) installed in Allison 250‑C28 engines when their serial numbers match those listed in the AD. It affects operators, owners and maintenance organisations. The action — effective 13 June 2002 — prevents blade/shroud tip fractures that can cause uncommanded engine shutdowns, eliminating a serious in‑flight risk."}},"importantCases":[],"_links":{"self":"/api/acts/ad-al-250-81-third-stage-turbine-wheels","history":"/api/acts/ad-al-250-81-third-stage-turbine-wheels/history","analysis":"/api/acts/ad-al-250-81-third-stage-turbine-wheels/analysis","conflicts":"/api/acts/ad-al-250-81-third-stage-turbine-wheels/conflicts","importantCases":"/api/acts/ad-al-250-81-third-stage-turbine-wheels/important-cases","documents":"/api/acts/ad-al-250-81-third-stage-turbine-wheels/documents"}}