{"id":"F2006B07456","name":"AD/TPE 331/45 - Third Stage Stator Assembly","slug":"ad-tpe-331-45-third-stage-stator-assembly","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":49803,"registerId":"commonwealth-F2006B07456-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/TPE 331/45 - Third Stage Stator Assembly","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 106 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nAlliedSignal (Garrett/AiResearch) Turbine Engines \\- TPE 331 Series\n\nAD/TPE 331/45 Third Stage Stator Assembly 2/93\n\nTX\n\nApplicability: TPE 331-1,-2,-2UA,-3U,-3UW,-5,5A,-6 and 6A Turboprop and TSE331-3U Turboshaft engines incorporating third stage stator assemblies Part Number 868379-3 repaired at National Flight Services (USA) between 20 Feb 1990 and 6 April 1992 and identified by serial numbers listed in National Flight Services Alert Bulletin NF331-A72-11921 dated 9 November 1992.\n\nRequirement: Replace Third Stage Stator assemblies Part Number 868379-3 repaired at National Flight Services (USA) between 20 Feb 1990 and 6 April 1992 and identified by serial numbers listed in National Flight Services Alert Bulletin NF331-A72-11921 dated 9 November 1992 with serviceable assemblies.\n\nNote: FAA Priority Letter AD 92-26-08 refers.\n\nCompliance: Replace affected Third Stage Stator assemblies with cycles in service since repair by National Flight Services in accordance with the following schedule:\n\n    900 or more cycles : replace within 50 cycles from 24 December 1992;\n\n    b. 450 to 899 cycles : replace within 150 cycles in service from 24 December 1992 but not to exceed 950 cycles; or\n\n    c. Less than 450 cycles: replace before accumulating 600 cycles.\n\n(Cracking of the third stage stator assemblies is related to operating cycles rather than operating hours. If cycles cannot be determined, calculate cycles by multiplying third stage stator assembly hours time in service by 1.5)\n\nBackground: The FAA advises of reports that a Hastelloy S material inner seal support in a third stage stator assembly fatigue cracked, moved aft and made contact with the third stage turbine wheel resulting in an uncontained engine failure. In reports of other incidents, several Hastelloy S material inner seal supports exhibited numerous circumferential cracks before achieving approved life limits. An undetermined number out of 283 third stage stator assemblies were repaired with Hastelloy S material instead of the approved Haynes 25 material at National Flight Services between 20 February 1990 and 6 April 1992. The FAA has determined that Hastelloy S has approximately one sixth the expected fatigue life in this application and, if not removed from service, can result in uncontained failure of the third stage turbine wheel.","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":3,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope. It addresses a specific manufacturing defect in a specific engine component from a specific repair facility during a defined time period. There is no evidence of scope creep; the directive remains tightly focused on the Hastelloy S material substitution issue as originally identified."},"complexity_factors":["Single, specific mechanical defect addressed (incorrect material in one component)","Clear applicability criteria: specific engine models, part numbers, repair facility, date range, and serial numbers","Straightforward compliance schedule with three distinct thresholds based on flight cycles","One simple calculation formula provided for missing data (hours × 1.5)","No nested exceptions or conditional logic beyond the three-tier replacement schedule","Limited cross-references: only one external document (FAA AD 92-26-08) and one manufacturer bulletin referenced","Technical but not legally complex — primarily operational/mechanical instructions"],"plain_english_summary":"This CASA Airworthiness Directive mandates replacement of certain third-stage stator assemblies in AlliedSignal (Garrett/AiResearch) TPE/TSE 331 engines that were repaired by National Flight Services (Feb 1990–Apr 1992) using Hastelloy S instead of approved Haynes 25. The incorrect material wears and can crack, risking uncontained engine failure.\n\nIt affects operators with those repaired parts (specific serial numbers listed in the bulletin) and sets compliance deadlines tied to flight-cycle history to prevent catastrophic engine damage."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"This AD is tightly focused on removing a specific set of third stage stator assemblies that were repaired with an incorrect material during a defined time window. It enforces short, part‑specific replacement deadlines tied to accumulated cycles. The measure does not broaden the regulatory reach beyond that original corrective purpose: it does not add new obligations for assemblies outside the listed serial numbers, nor does it create ongoing surveillance obligations beyond the replacement requirement. Therefore the scope has not grown significantly beyond its original, corrective intent (see Applicability; Requirement; Background)."},"complexity_factors":["Applicability depends on matching part number (P/N 868379-3) AND repair location/date AND serial numbers listed in an external Alert Bulletin (NF331-A72-11921).","Three-tiered conditional compliance schedule based on cycles since repair (>=900; 450–899; <450).","Fallback calculation for cycles where cycles are unknown (multiply hours by 1.5).","Cross-reference to an external FAA Priority Letter AD (FAA AD 92-26-08) and an external Alert Bulletin increases procedural steps for operators.","Multiple engine model variants covered (TPE 331-1,-2,-2UA,-3U,-3UW,-5,5A,-6 and 6A, and TSE331-3U) requiring fleet checks across models.","Serial-number‑specific applicability (list not reproduced in the AD text) requiring operators to consult the separate bulletin."],"plain_english_summary":"**What this directive does, in plain English**\n\n- This Airworthiness Directive (AD) orders the replacement of certain third stage stator assemblies (part number 868379-3) in specified AlliedSignal (Garrett/AiResearch) TPE 331 turboprop and TSE331 turboshaft engines. (A third stage stator assembly is a stationary part in the turbine section of the engine.)\n\n- It only applies to those assemblies that were repaired at National Flight Services (USA) between 20 February 1990 and 6 April 1992 and are identified by serial numbers listed in National Flight Services Alert Bulletin NF331-A72-11921 dated 9 November 1992. (The AD therefore targets a specific set of repaired parts, not every engine of these models.)\n\n- The AD requires operators to replace the affected assemblies with a serviceable assembly according to a short schedule based on the number of operating cycles (see the Compliance section below). If an operator cannot determine cycles directly, the AD instructs operators to estimate cycles by multiplying the assembly hours in service by 1.5. (The AD treats fatigue risk as a function of cycles rather than hours.)\n\n**Who this affects**\n\n- Aircraft owners/operators who have TPE 331 or TSE331 engines of the listed models that contain a third stage stator assembly P/N 868379-3 repaired at National Flight Services in the specified date window, and maintenance organisations that service those engines.\n\n**Why the AD was issued (official rationale, and what that implies mechanically)**\n\n- The FAA reported that some third stage stator inner seal supports, which in the affected repairs were made from Hastelloy S instead of the approved Haynes 25, developed fatigue cracks, moved aft and contacted the third stage turbine wheel. That contact can lead to uncontained engine failure. The FAA estimated Hastelloy S has roughly one-sixth the expected fatigue life in this application. (Background)\n\n- Mechanically, the AD removes suspected low‑fatigue-life assemblies from service ahead of their usual life limits: it forces replacement within a short number of cycles depending on how many cycles the assembly has already accumulated since the erroneous repair. (Requirement; Compliance)\n\n**Compliance timing required by the AD**\n\n- If the affected assembly has 900 or more cycles since the repair: replace within 50 cycles from 24 December 1992.\n- If it has 450–899 cycles: replace within 150 cycles from 24 December 1992, but not to exceed 950 cycles total life.\n- If it has fewer than 450 cycles: replace before it reaches 600 cycles.\n- If cycles are unknown: estimate cycles = hours in service × 1.5. (Compliance)\n\n**Who pays and who decides**\n\n- Aircraft owners/operators pay for the replacement parts, labour and associated downtime. The operator decides how and where to procure the serviceable assemblies (new, or correctly repaired at an approved facility) but must meet the AD’s timing and part requirements. The regulator (Civil Aviation Safety Authority via the AD and referenced FAA information) enforces compliance. (Applicability; Requirement; Compliance)\n\n**Immediate implementation costs and operational effects**\n\n- Direct costs: purchase or repair of compliant stator assemblies, replacement labour and aircraft downtime while the replacement is carried out.\n- Compliance burden: identifying whether an installed assembly is on the affected serial‑number list, determining cycles (or estimating them from hours), and scheduling the maintenance within the AD’s short deadlines. (Applicability; Compliance)\n\n**Supply, market and competition effects to note**\n\n- The AD concentrates demand for serviceable third stage stator assemblies or approved repair services among a defined group of operators. That can increase short‑term demand for parts or approved repair capacity and lead to higher prices or longer lead times for replacements.\n- Independent repair shops and authorised service centres that can supply correctly manufactured or repaired assemblies may gain business; proprietors of the assemblies repaired incorrectly (National Flight Services) may face reputational and commercial consequences. (Background; Requirement)\n\n**Trade-offs, risks and implementation issues**\n\n- Trade-offs: the AD reduces the risk of uncontained failures by removing suspect components early, at the cost of maintenance expenditure and aircraft downtime.\n- Verification risk: operators must check serial numbers against an external alert bulletin (NF331‑A72‑11921) and may need administrative support from maintenance organisations to confirm eligibility.\n- Substitution risk: if serviceable assemblies are scarce, operators may delay flights or seek alternative repairs, which could increase indirect costs or create logistical bottlenecks.\n\n**Source claims and how they are used**\n\n- The AD cites FAA incident reports and a determination about Hastelloy S fatigue life as the technical basis for early removal of the affected parts (Background). Those technical findings function here as the safety justification for mandatory replacement; the AD implements that removal via the replacement and timing rules above (Requirement; Compliance)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-tpe-331-45-third-stage-stator-assembly","history":"/api/acts/ad-tpe-331-45-third-stage-stator-assembly/history","analysis":"/api/acts/ad-tpe-331-45-third-stage-stator-assembly/analysis","conflicts":"/api/acts/ad-tpe-331-45-third-stage-stator-assembly/conflicts","importantCases":"/api/acts/ad-tpe-331-45-third-stage-stator-assembly/important-cases","documents":"/api/acts/ad-tpe-331-45-third-stage-stator-assembly/documents"}}