{"id":"F2006B07398","name":"AD/TFE 731/15 - HP Turbine Rotor Disc","slug":"ad-tfe-731-15-hp-turbine-rotor-disc","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":49601,"registerId":"commonwealth-F2006B07398-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/TFE 731/15 - HP Turbine Rotor Disc","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/TFE731/15 HP Turbine Rotor Disc 12/88 DM\n\nApplicability: TFE 731-3 series engines which may have suspect HP turbine rotor discs whose S/No are listed in the Requirement document.\n\nRequirement: Remove from service specific serial numbered HP turbine rotor disc Part No.\n\n3072316-2/-3 and 3073110-1/-2 in accordance with GTEC Alert SB TFE 731-A72 \\- 3376.\n\nNote: FAA AD Priority Letter 88-18-03 refers.\n\nCompliance: Within 25 engine operating cycles after 22 September 1988.\n\nBackground: This Directive is issued following advice from the manufacturer that some HP turbine rotor discs have incorrect curvic coupling tooth root fillet radii. This Directive is required to prevent uncontained HP turbine disc failures which could occur on engines containing suspect reworked discs.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive issued in 1988 addressing a specific manufacturing defect. It has not expanded beyond its original narrow scope of removing defective HP turbine rotor discs from TFE731-3 engines."},"complexity_factors":["Single, specific technical requirement with clear part numbers and serial numbers","Only one compliance condition (25 engine operating cycles)","No nested exceptions or conditional logic","Minimal cross-referencing (only to manufacturer service bulletin and FAA equivalent)","Short document (approximately 150 words)","Only 2 defined part numbers and reference to one external document"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) that requires specific maintenance action on aircraft engines.\n\n**What it does:**\nOrders the immediate removal from service of certain high-pressure (HP) turbine rotor discs in AlliedSignal TFE731-3 series jet engines. These discs are critical components that spin at extremely high speeds in the \"hot section\" of the engine.\n\n**Who it affects:**\nOwners and operators of aircraft powered by TFE731-3 series engines (commonly used in business jets) that have specific serial-numbered rotor discs installed.\n\n**Why it matters:**\nThe manufacturer discovered that some discs were manufactured with incorrect \"curvic coupling\" tooth root fillet radii — essentially, a machining defect in the interlocking teeth that connect disc sections. If these defective discs fail, they can cause \"uncontained\" failures where high-speed metal fragments escape the engine casing, potentially damaging the aircraft or injuring occupants. The directive gives operators just **25 engine operating cycles** (roughly 25 flights) to comply after 22 September 1988.\n\n**Key terms explained:**\n- **Curvic coupling:** A precision-machined, curved-tooth connection used to join rotating engine components\n- **Uncontained failure:** When an engine failure releases debris outside the engine's protective casing\n- **Airworthiness Directive (AD):** A legally enforceable safety order that must be followed to keep an aircraft certified as airworthy"},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The instrument sets a targeted, technical requirement for removal of specified HP turbine rotor discs from TFE731-3 engines and does not indicate any change of scope from an earlier or different intent within the text provided. Applicability limits the Directive to engines containing the serial-numbered discs listed in the Requirement document, and the Requirement prescribes removal per the manufacturer’s service bulletin within a fixed compliance window. (Applicability; Requirement; Compliance)"},"complexity_factors":["Narrow technical scope limited to specific engine model (TFE731-3) and listed serial-numbered parts (Part Nos. 3072316-2/-3 and 3073110-1/-2). (Applicability; Requirement)","Short compliance deadline: within 25 engine operating cycles after 22 September 1988, creating scheduling pressure. (Compliance)","Dependence on an external manufacturer service bulletin (GTEC Alert SB TFE 731-A72-3376) for the prescribed removal procedure. (Requirement)","Need for accurate serial-number identification and record checks before remedial action can be taken. (Applicability; Requirement)","Potential operational logistics (coordinating maintenance, sourcing replacements, downtime) implied though not detailed in the text. (Requirement; Compliance)","Cross-reference to foreign authority (FAA AD Priority Letter) which may be relied on for context but does not alter procedural requirements in the text. (Note)"],"plain_english_summary":"CASA orders removal from service of specific serial-numbered high‑pressure turbine rotor discs (Part Nos. 3072316-2/-3, 3073110-1/-2) in AlliedSignal TFE731-3 engines because reworked curvic tooth root fillet radii may cause uncontained failures. Operators and maintenance organisations must follow the manufacturer’s GTEC Alert Service Bulletin and complete removals within 25 engine operating cycles. The rule is narrowly targeted; compliance, downtime and replacement costs fall to affected operators."}},"importantCases":[],"_links":{"self":"/api/acts/ad-tfe-731-15-hp-turbine-rotor-disc","history":"/api/acts/ad-tfe-731-15-hp-turbine-rotor-disc/history","analysis":"/api/acts/ad-tfe-731-15-hp-turbine-rotor-disc/analysis","conflicts":"/api/acts/ad-tfe-731-15-hp-turbine-rotor-disc/conflicts","importantCases":"/api/acts/ad-tfe-731-15-hp-turbine-rotor-disc/important-cases","documents":"/api/acts/ad-tfe-731-15-hp-turbine-rotor-disc/documents"}}