{"id":"F2006B07405","name":"AD/TFE 731/25 - Low Pressure Turbine Nozzle A5 Airseal","slug":"ad-tfe-731-25-low-pressure-turbine-nozzle-a5-airseal","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":49625,"registerId":"commonwealth-F2006B07405-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/TFE 731/25 - Low Pressure Turbine Nozzle A5 Airseal","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 \\- TFE731 Series\n\nAD/TFE731/25 Low Pressure Turbine Nozzle A5 Airseal 11/94 DM\n\nApplicability: TFE731-3 series engines not incorporating Allied Signal Service Bulletin TFE731- 72-3502 or TFE731-72-3509 as applicable.\n\nRequirement: Replace the low pressure turbine nozzle A5 airseal in accordance with Allied Signal Service Bulletin TFE731-72-3502 or TFE731-72-3509 as applicable.\n\nNote: This Directive provides the terminating action for CAO105 Airworthiness Directives, AD/HS125/130 Amdt 1, AD/IAI-W/16 Amdt 1 and AD/CESSNA 650/5.\n\nCompliance: Effective 14 September 1994:\n\nAirseals with less than 500 hours total time in service since new; prior to accumulating 650 hours total time in service.\n\nAirseals with more than 500 hours total time in service since new; within 150 hours time in service.\n\nBackground: This Directive has been issued to require replacement of certain low pressure turbine nozzle A5 airseals. The requirement follows reports of uncontained 1st stage low pressure turbine disc failures in AlliedSignal TFE731-3 engines.\n\nThe turbine disc failures were attributed to failure of the A5 airseal.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"This Directive consolidates and replaces several earlier airworthiness directives by providing a single mandated replacement action for the A5 airseal; it narrows ongoing obligations to engines that have not already complied with the specified AlliedSignal service bulletins and thus shifts enforcement from multiple ADs to this single, bulletin-driven requirement (Note/Applicability/Requirement)."},"complexity_factors":["Narrow technical applicability: applies only to TFE731-3 engines not incorporating specific AlliedSignal service bulletins (Applicability).","Mandates compliance by reference to manufacturer service bulletins rather than prescribing an alternate procedure (Requirement).","Time-in-service thresholds create two different compliance windows based on existing hours-since-new (Compliance).","Acts as terminating action for several prior directives, consolidating obligations (Note).","Safety-critical component replacement is straightforward mechanically but requires tracking component hours and arranging parts/work (Background)."],"plain_english_summary":"This airworthiness directive requires owners/operators of AlliedSignal TFE731-3 engines (that have not implemented the specified AlliedSignal service bulletins) to replace the low-pressure turbine nozzle A5 airseal. Compliance must follow the named service bulletin and meets set time-in-service windows (replace before 650 hours if the airseal has <500 hours, or within 150 hours if >500). The Civil Aviation Safety Authority issued it after failures were linked to A5 airseal breakdown."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific mechanical failure mode in a specific engine series. It has not expanded beyond its original purpose of mandating replacement of a defective component."},"complexity_factors":["Single, specific mechanical component targeted (A5 airseal)","Simple binary applicability test (whether specific service bulletins have been incorporated)","Two-tier compliance schedule based on hours-in-service threshold (500 hours)","No nested definitions or extensive cross-referencing to other legislation","Self-contained document with clear background explanation","Terminating action for 4 previous directives, but this is clearly stated rather than requiring external research"],"plain_english_summary":"This AD mandates replacement of the low-pressure turbine nozzle A5 airseal on AlliedSignal TFE731-3 series engines for operators that haven’t already complied with specified service bulletins, affecting aircraft such as HS125, IAI Westwind and Cessna Citation 650. \n\nIt responds to airseal failures that led to uncontained turbine disc breakups — a severe safety hazard — and sets short compliance windows based on the airseal’s hours in service."}},"importantCases":[],"_links":{"self":"/api/acts/ad-tfe-731-25-low-pressure-turbine-nozzle-a5-airseal","history":"/api/acts/ad-tfe-731-25-low-pressure-turbine-nozzle-a5-airseal/history","analysis":"/api/acts/ad-tfe-731-25-low-pressure-turbine-nozzle-a5-airseal/analysis","conflicts":"/api/acts/ad-tfe-731-25-low-pressure-turbine-nozzle-a5-airseal/conflicts","importantCases":"/api/acts/ad-tfe-731-25-low-pressure-turbine-nozzle-a5-airseal/important-cases","documents":"/api/acts/ad-tfe-731-25-low-pressure-turbine-nozzle-a5-airseal/documents"}}