{"id":"F2008L04512","name":"AD/TFE 731/36 - Interstage Turbine Transition Duct","slug":"ad-tfe-731-36-interstage-turbine-transition-duct","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":76558,"registerId":"commonwealth-F2008L04512-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"AlliedSignal (Garrett/AiResearch) Turbin","sectionType":"division","heading":"AlliedSignal (Garrett/AiResearch) Turbine Engines - TFE731 Series","content":"### AlliedSignal (Garrett/AiResearch) Turbine Engines - TFE731 Series\n\n| AD/TFE 731/36 | Interstage Turbine Transition Duct | 13/2008 |\n| ------------- | ---------------------------------- | ------- |\n\n| Applicability: | Honeywell International Inc. TFE731-4, -4R, -5, -5AR, -5BR, and -5R series turbofan engines, with interstage turbine transition (ITT) duct, part number (P/N) 3075292-1, 3075292-3, 3074766-1, 3077063-1, 3075655-1, 3075655-2, 3075699-1, or3075699-3, installed.Note 1: These engines are installed on, but not limited to, Avions Marcel Dassault Mystere-Falcon 50 series, Dassault-Aviation 20, 50, 900, MF900 series, Cessna Model 650, Cessna Citation VII, and Raytheon Corporate Jets (formerly British Aerospace) Hawker 800 and 850XP series aeroplanes.                                                                                                                                                                                          |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n| Requirement:   | 1. Replace the affected ITT ducts listed by part number in the applicability section of this AD, with a serviceable and redesigned ITT duct.2. Do not install any ITT duct listed by P/N in paragraph (c) of this AD, onto any engine.DefinitionsFor the purpose of this AD, a serviceable and redesigned ITT duct is one not having a part number listed in this AD.For the purpose of this AD, next access of the ITT duct is when the ITT duct is removed from the engine.Related InformationHoneywell International Inc. Service Bulletin (SB) No. TFE731-72-3727, dated12 September 2007, and SB No. TFE731-72-3728, dated 12 September 2007, pertain to the subject of this AD.Note 2: FAA AD 2008-19-12 Amdt 39-15679 dated 12 September 2008 refers. |\n| Compliance:    | For Requirement 1 - At the next Major Periodic Inspection of the engine or at next access of the ITT duct, whichever occurs first, but not to exceed 2,600 hours time-in-service after the effective date of this AD, unless the actions have already been done.For Requirement 2 - After the effective date of this AD.                                                                                                                                                                                                                                                                                                                                                                                                                                     |\n\n|             | This Airworthiness Directive becomes effective on 18 December 2008.                                                                                                                                                                                                                                                                                                                                                                                                                 |\n| ----------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Background: | This AD results from reports of 49 low-pressure turbine (LPT) blade separation events. Six of those events resulted in circumferential failure of the LPT2 or LPT3 nozzle assembly, leading to deformation of the ITT duct and uncontainment of the turbine blades and fragments of the LPT nozzle assembly. The issuing of this AD is intended to prevent uncontainment of turbine blades and fragments of the LPT nozzle assembly, which could result in damage to the aeroplane. |\n\n![](image.001.png)  \nJames Coyne  \nDelegate of the Civil Aviation Safety Authority\n\n6 November 2008","sortOrder":0},{"sectionNumber":"AD/TFE 731/36","sectionType":"part","heading":"AD/TFE 731/36","content":"## AD/TFE 731/36","sortOrder":1},{"sectionNumber":"Interstage Turbine Transition Duct","sectionType":"part","heading":"Interstage Turbine Transition Duct","content":"## Interstage Turbine Transition Duct","sortOrder":2},{"sectionNumber":"13/2008","sectionType":"part","heading":"13/2008","content":"## 13/2008","sortOrder":3}],"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":3,"scope_assessment":{"changed":false,"description":"This AD remains narrowly focused on mitigating the specific risk of LPT blade separations causing ITT duct deformation and uncontainment. It does not broaden into unrelated maintenance mandates or new certification rules. The measures (replacement and installation ban for listed P/Ns) match the stated safety purpose and do not materially expand the AD beyond that original intent."},"complexity_factors":["Short instrument (single AD) with focused scope on specific part numbers","List of 8 specific affected ITT duct part numbers in applicability","Two mandatory actions (replace at specified trigger; prohibition on future installation)","Timing condition with two triggers: next Major Periodic Inspection OR next access, whichever first, and an absolute limit of 2,600 hours","Definition of key terms inside the AD (serviceable and redesigned; next access)","Cross-references to two Honeywell service bulletins and a related FAA AD"],"plain_english_summary":"**What this rule does (mechanically)**\n\n- It requires owners/operators of certain Honeywell (AlliedSignal/Garrett/AiResearch) TFE731 series turbofan engines to remove and replace specific interstage turbine transition (ITT) ducts (identified by part numbers) with a redesigned, serviceable ITT duct. (Requirement 1)\n- It also bans installing any of the affected ITT duct part numbers listed in the AD onto any engine after the AD’s effective date. (Requirement 2)\n\n**Which engines and aeroplanes are affected**\n\n- Applies to Honeywell TFE731-4, -4R, -5, -5AR, -5BR and -5R engines that have one of the listed ITT duct part numbers installed. (Applicability)\n- Those engines are fitted to, but not limited to, Dassault Falcon 20/50/900/MF900, Cessna Model 650 and Citation VII, and Hawker 800/850XP family aeroplanes. (Applicability)\n\n**When the work must be done**\n\n- Replace the listed ITT ducts at the engine’s next Major Periodic Inspection or at the next access to the ITT duct (defined as when the ITT duct is removed from the engine), whichever comes first, and no later than 2,600 hours time-in-service after the AD’s effective date — unless the replacement has already been done. (Compliance)\n- The installation ban on the listed part numbers applies immediately after the AD’s effective date. (Requirement 2 / Compliance)\n\n**Why the regulator issued this AD (stated reason and mechanical effect)**\n\n- The AD follows reports of 49 low-pressure turbine (LPT) blade separations; six events caused circumferential failure of the LPT nozzle assembly. Those failures deformed the ITT duct and allowed turbine blades and nozzle fragments to escape containment. The AD aims to prevent uncontainment of turbine blades and fragments that could damage the aeroplane. (Background)\n\n**Who pays and who decides**\n\n- Aircraft/engine operators (owners or their maintenance organisations) pay for the replacement parts, labour and associated downtime. Operators also decide the scheduling of the replacement within the mandated timing (next major inspection / next access, or within 2,600 hours).\n- The regulator enforces the AD and the effective date fixes the legal obligation to comply. The AD also references Honeywell service bulletins for technical detail. (Related Information)\n\n**Practical compliance and implementation notes**\n\n- A “serviceable and redesigned” ITT duct is defined as any ITT duct not carrying one of the prohibited part numbers listed in the AD (Definitions). That means operators can comply by installing any acceptable replacement duct that is not one of the listed P/Ns.\n- The AD cross-references Honeywell Service Bulletins (SB TFE731-72-3727 and SB TFE731-72-3728) for the technical replacement procedures and to FAA AD 2008-19-12. Operators should follow the manufacturer’s SB for the work method and inspection details. (Related Information)\n\n**Cost, incentives and trade-offs (mechanical effects on behaviour and markets)**\n\n- Direct costs: purchase price of redesigned ITT ducts, labour charges, and aircraft downtime while the engine is accessed/inspected. Those costs are borne by operators or their insurers/lessors.\n- Timing incentive: because replacement is required at next access or major inspection (or within 2,600 hours), operators can schedule the work to coincide with planned maintenance to limit extra downtime; some operators may choose earlier access if they judge the risk unacceptable.\n- Supply risk: if many operators need redesigned ITT ducts in a short period, parts availability and lead times could increase, raising short-run costs and potential grounding delays.\n- Compliance burden: maintenance organisations must track affected engines, part numbers, and ensure no prohibited P/N is installed after the effective date. Record-keeping and traceability of parts become important.\n- Safety trade-off: the AD imposes an immediate parts ban and mandatory replacement to reduce the risk of uncontainment. That reduces the risk of in-flight damage but imposes concentrated costs on affected operators.\n\n**Implementation risk and enforcement**\n\n- Key implementation risks are parts supply constraints and correct identification of ITT duct part numbers during inspections.\n- Enforcement is through the regulator’s airworthiness compliance regime. Operators who fail to replace the prohibited parts within the defined time window remain at regulatory risk and continue to operate with the identified failure risk.\n\n**Where to find technical detail**\n\n- The Honeywell service bulletins cited in the AD contain the procedural and technical replacement detail; the AD sets the mandatory timing and the prohibition on installation of the listed P/Ns. (Related Information)\n\n(References: Applicability; Requirement 1 and 2; Definitions; Compliance; Background; Related Information.)"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This AD maintains its original narrow scope: addressing a specific mechanical failure mode in specific engine models. The directive targets exactly the safety issue identified in the background (ITT duct deformation leading to uncontainment) without expanding into unrelated operational or maintenance requirements."},"complexity_factors":["Short, single-purpose directive with only 2 substantive requirements","Limited applicability: 6 specific engine models and 8 specific part numbers","Clear compliance timeline with single condition (next inspection/access, capped at 2,600 hours)","Minimal cross-referencing: only 2 Honeywell service bulletins and 1 FAA AD mentioned in notes","Simple definitions section with only 2 defined terms ('serviceable and redesigned ITT duct' and 'next access')","No nested exceptions or conditional logic beyond the compliance deadline calculation"],"plain_english_summary":"This mandatory CASA Airworthiness Directive affects Honeywell TFE731 engines on business jets (e.g., Dassault, Cessna, Hawker). It responds to multiple turbine blade failures that can deform the Interstage Turbine Transition (ITT) duct and allow hazardous uncontained debris.\n\nOperators must replace the affected ITT ducts with redesigned serviceable units by the next major engine inspection or within 2,600 flight hours, whichever comes first, and must not install the old duct part numbers once the AD is in force."}},"importantCases":[],"_links":{"self":"/api/acts/ad-tfe-731-36-interstage-turbine-transition-duct","history":"/api/acts/ad-tfe-731-36-interstage-turbine-transition-duct/history","analysis":"/api/acts/ad-tfe-731-36-interstage-turbine-transition-duct/analysis","conflicts":"/api/acts/ad-tfe-731-36-interstage-turbine-transition-duct/conflicts","importantCases":"/api/acts/ad-tfe-731-36-interstage-turbine-transition-duct/important-cases","documents":"/api/acts/ad-tfe-731-36-interstage-turbine-transition-duct/documents"}}