{"id":"F2006B07412","name":"AD/TFE 731/6 - High Pressure Rotor and Nozzle Assembly Bolt - Replacement","slug":"ad-tfe-731-6-high-pressure-rotor-and-nozzle-assembly-bolt-replacement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":49646,"registerId":"commonwealth-F2006B07412-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/TFE 731/6 - High Pressure Rotor and Nozzle Assembly Bolt - Replacement","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-generator: Aspose.Words for .NET 22.10.0\n---\n\n?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"no\"?>\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  AlliedSignal (Garrett/AiResearch) Turbine Engines - TFE731 Series\n\n \n\n# AD/TFE731/6 High Pressure Rotor and Nozzle Assembly Bolt - Replacement\n\nApplicability: TFE731-2-1C; TFE731-2-2B; TFE731-2-2J; TFE731-2-2L.\n\n \n\nDocument: AiResearch SB No. 72-3138, or AD/AIR-T/38.\n\n# 3/86\n\n \n\nCompliance: During the next hot end inspection completed after 30 September 1980 or during the next unscheduled exposure of the area, whichever occurs first.\n\n \n\nBackground: This Directive is issued to reduce the possibility of damaging the curvic coupling and the forward side of the H.P. turbine rotor by pieces of failed bolts.\n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific mechanical defect in specific engine models. It has not expanded beyond its original purpose of mandating bolt replacement to prevent turbine damage."},"complexity_factors":["Single, specific mechanical issue addressed (bolt replacement)","Only 4 engine variants affected, clearly listed","Single compliance deadline with straightforward trigger (next inspection or exposure)","No nested exceptions or conditional logic","No defined terms section — uses standard aviation terminology","Short document (approximately 150 words of substantive content)","References external technical document (Service Bulletin 72-3138) for actual procedure"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for aircraft engines.\n\n**What it does:**\nOrders owners and operators of specific AlliedSignal (Garrett/AiResearch) TFE731 jet engines to replace certain bolts in the high-pressure rotor and nozzle assembly.\n\n**Who it affects:**\nAnyone operating aircraft with these specific engine models: TFE731-2-1C, TFE731-2-2B, TFE731-2-2J, or TFE731-2-2L. These are commonly used in business jets like the Learjet 35/36 and Dassault Falcon 10.\n\n**Why it matters:**\nThe bolts can fail and break apart. When they do, flying metal fragments can destroy the \"curvic coupling\" (a precision gear-like connection between engine parts) and damage the high-pressure turbine rotor. This could cause catastrophic engine failure in flight.\n\n**When to comply:**\nDuring the next \"hot end inspection\" (maintenance check of the hot section of the engine) after 30 September 1980, or the next time that area is opened up for any reason — whichever comes first.\n\n**The bottom line:**\nThis is a critical safety fix. If you don't replace these bolts, your engine could disintegrate."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive's scope is consistent with its stated purpose in the text: it targets specified TFE731 engine models and requires bolt replacement to reduce the risk of turbine rotor and curvic coupling damage. The instrument sets a clear applicability and a single compliance trigger tied to inspection/exposure; it does not expand or narrow that scope within the provided text."},"complexity_factors":["Narrow technical scope: applies only to four specific engine models (Applicability)","Single, discrete required action (bolt replacement) but technical details are deferred to an external service bulletin (Document)","Fixed compliance rule tied to inspection timing or unscheduled exposure (Compliance) reduces legal ambiguity but requires operational scheduling","Dependence on availability and correctness of the referenced service bulletin adds practical complexity","Limited interpretive ambiguity around terms like “hot end inspection” and “unscheduled exposure” for operators and maintainers"],"plain_english_summary":"What this directive requires\n\n- This airworthiness directive requires replacement of the high pressure rotor and nozzle assembly bolts on certain AlliedSignal (Garrett/AiResearch) TFE731 turbine engines. The engine models listed are TFE731-2-1C, TFE731-2-2B, TFE731-2-2J and TFE731-2-2L. (Applicability)\n- The replacement work should follow the referenced service document: AiResearch Service Bulletin No. 72-3138, or AD/AIR-T/38. (Document)\n- When to do it: the replacement must be done during the next \"hot end\" inspection that is completed after 30 September 1980, or at the next unscheduled exposure of the area, whichever happens first. (Compliance)\n\nWhy the directive exists (official rationale)\n\n- The directive's stated purpose is to reduce the possibility that failed bolt fragments will damage the curvic coupling and the forward side of the high‑pressure turbine rotor. (Background)\n\nWho is affected and who pays\n\n- Aircraft owners and operators of the listed TFE731 engine models are the primary parties affected. They must arrange for the inspection/exposure and the bolt replacement. (Applicability; Compliance)\n- Operators will bear the direct costs: parts, labour, and any aircraft downtime while the work is carried out. Maintenance organisations performing the work incur labour costs but receive the maintenance revenue.\n- The directive refers operators to a manufacturer's service bulletin for the technical steps and parts. Following that bulletin may require purchasing specified replacement bolts or kits. (Document)\n\nHow it changes behaviour and decisions\n\n- Operators must plan to replace the specified bolts at the next scheduled hot end inspection after the stated date, or sooner if the relevant area is exposed unexpectedly. This changes maintenance scheduling and may advance work that would otherwise wait until a later inspection. (Compliance)\n- Maintenance providers must carry out the bolt replacement per the service bulletin and may need to stock or source the replacement parts. (Document)\n\nCosts, incentives and trade‑offs to note\n\n- Cost vs. avoided damage: the immediate cost is parts and labour for replacement and any aircraft downtime; the stated benefit is reduced risk of rotor/curvic coupling damage, which would be more expensive to repair. (Background)\n- Scheduling trade‑off: requiring action at the next hot end inspection or at the next unscheduled exposure forces earlier intervention when that inspection or exposure occurs, which increases the chance of near‑term maintenance downtime.\n- Supply and implementation risk: successful compliance depends on availability of the specified replacement bolts and on correctly following the service bulletin instructions. If parts are scarce or the procedure is not followed precisely, the intended risk reduction may not occur. (Document)\n\nRegulatory decision and discretion\n\n- The directive is issued by the Civil Aviation Safety Authority as an airworthiness directive under the Civil Aviation Regulations framework shown in the header. It specifies mandatory compliance timing and references the service bulletin for technical detail. (Header; Compliance; Document)\n\nPractical compliance burdens\n\n- Operators must monitor inspection schedules to ensure the replacement occurs at the next hot end inspection after the date specified, or at the next unscheduled exposure. They must allocate funds for parts and labour and accept the operational downtime required to perform the replacement. (Compliance; Document)\n\nConcrete mechanics (how it is to be done)\n\n- The directive points operators to AiResearch SB No. 72-3138 (or AD/AIR-T/38) for the actual replacement procedure and parts list. The directive itself sets the timing and applicability rather than reproducing the technical steps. (Document)\n\nSource citations\n\n- Applicability: lists affected engine models. (Applicability)\n- Required document: AiResearch SB No. 72-3138, or AD/AIR-T/38. (Document)\n- Compliance timing: next hot end inspection after 30 September 1980 or next unscheduled exposure. (Compliance)\n- Stated purpose: reduce possibility of damaging curvic coupling and forward side of H.P. turbine rotor by bolt fragments. (Background)\n"}},"importantCases":[],"_links":{"self":"/api/acts/ad-tfe-731-6-high-pressure-rotor-and-nozzle-assembly-bolt-replacement","history":"/api/acts/ad-tfe-731-6-high-pressure-rotor-and-nozzle-assembly-bolt-replacement/history","analysis":"/api/acts/ad-tfe-731-6-high-pressure-rotor-and-nozzle-assembly-bolt-replacement/analysis","conflicts":"/api/acts/ad-tfe-731-6-high-pressure-rotor-and-nozzle-assembly-bolt-replacement/conflicts","importantCases":"/api/acts/ad-tfe-731-6-high-pressure-rotor-and-nozzle-assembly-bolt-replacement/important-cases","documents":"/api/acts/ad-tfe-731-6-high-pressure-rotor-and-nozzle-assembly-bolt-replacement/documents"}}