{"id":"F2008L01253","name":"AD/TFE731/35 - High Pressure Turbine Rotor Discs Curvic Couplings","slug":"ad-tfe731-35-high-pressure-turbine-rotor-discs-curvic-couplings","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":73491,"registerId":"commonwealth-F2008L01253-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 731/35 | High Pressure Turbine RotorDiscs Curvic Couplings | 5/2008 |\n| ------------- | ------------------------------------------------- | ------ |\n\n| Applicability: | Honeywell International Inc. (Honeywell) TFE731-2C, -3B, -3BR, -3C, -3CR, -3D,-3DR, -4R, -5AR, -5BR, -5R, -20R, -20AR, -20BR, -40, -40AR, -40R, and -60 series turbofan engines.Note 1: These engines are installed on, but not limited to Avions Marcel Dassault Mystere-Falcon 10 and 50 Series, Cessna Model 650, Citations III, VI, and VII, Dassault-Aviation 20, 50, 50EX, 900, MF900, and 900EX (900DX) Series, Gulfstream Aerospace LP (formerly IAI) 1125 Westwind Astra, Astra SPX, Gulfstream 100 Series Israel Aircraft Industries (IAI) 1124 Series (Westwind 1124), Learjet 31, 35, 36, 45 (or Learjet 40), and 55 Series, Lockheed-Georgia 3329-25 Series (731 Jetstar, Jetstar II), Raytheon Corporate Jets (formerly British Aerospace) Hawker 800 and 850 Series Sabreliner NA-265-65 (Sabreliner 65) aeroplanes.                                                                                                                                                                                                                                                                                            |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n| Requirement:   | 1. For TFE731-2C, -3B, -3BR, -3C, -3CR, -3D, -3DR, -4R, -5AR, -5BR, and -5R series turbofan engines, remove HP turbine rotor assemblies from service containing HP turbine rotor discs, part number (P/N) 3075772-1, having any serial number (SN) in Table 1 of Honeywell Service Bulletin (SB) No.TFE731-72-3720, dated 5 July 2006.2. For TFE731-20R, -20AR, -20BR, -40, -40AR, -40R, and -60 series turbofan engines, remove HP turbine rotor assemblies from service containing HP turbine rotor discs, P/N 3060841-1, having any SN in Table 1 of Honeywell Alert SB No. TFE731-A72-5185, dated 5 July 2006.3. HP turbine rotor discs removed per Requirements 1 or 2 of this AD must pass a curvic root radius inspection performed by Honeywell Engines, Systems and Services, Phoenix, Arizona, Certificate Repair Station No. ZN3R030M before the discs are eligible for reinstallation in an engine.For the purposes of this AD, access to the HP turbine rotor discs is defined as the removal of the HP turbine rotor assembly from the engine.Note 2: FAA AD 2008-02-19 Amdt 15349 dated 16 January 2008 refers. |\n\n| Compliance: | 1. For TFE731-2C, -3B, -3BR, -3C, -3CR, -3D, -3DR, -4R, -5AR, -5BR, and -5R series turbofan engines use the following drawdown schedule:a. For HP turbine discs with 4,200 cycles-since-new (CSN) or more on the effective date of this AD, remove HP turbine rotor assemblies within 100 cycles-in-service (CIS) after the effective date of this AD.b. For HP turbine discs with fewer than 4,200 CSN on the effective date of this AD, remove HP turbine rotor assemblies at the next access to the HP turbine rotor discs, but not to exceed 4,300 CSN.2. For TFE731-20R, -20AR, -20BR, -40, -40AR, -40R, and -60 series turbofan engines use the following drawdown schedule:a. For HP turbine discs with 3,200 CSN or more on the effective date of this AD, remove HP turbine rotor assemblies within 100 CIS after the effective date of this AD.b. For HP turbine discs with fewer than 3,200 CSN on the effective date of this AD, remove HP turbine rotor assemblies at the next access to the turbine rotor discs, but not to exceed 3,300 CSN.3. From the effective date of this AD. |\n| ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n|             | This Airworthiness Directive becomes effective on 8 May 2008.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |\n| Background: | This AD results from the manufacturer's report that some HP turbine rotor discs received improperly machined radii in the root of the forward and aft curvic teeth during manufacture. The issuing of this AD is intended to prevent uncontained failure of the HP turbine rotor assembly, which could result in damage to the aeroplane.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |\n\n![](image.001.png)  \nDavid Punshon  \nDelegate of the Civil Aviation Safety Authority\n\n6 March 2008","sortOrder":0},{"sectionNumber":"AD/TFE 731/35","sectionType":"part","heading":"AD/TFE 731/35","content":"## AD/TFE 731/35","sortOrder":1},{"sectionNumber":"High Pressure Turbine RotorDiscs Curvic ","sectionType":"part","heading":"High Pressure Turbine RotorDiscs Curvic Couplings","content":"## High Pressure Turbine Rotor  \nDiscs Curvic Couplings","sortOrder":2},{"sectionNumber":"5/2008","sectionType":"part","heading":"5/2008","content":"## 5/2008","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":6,"scope_assessment":{"changed":false,"description":"This AD remains tightly focused on its original technical purpose: to address improperly machined curvic root radii on specific HP turbine rotor discs and to prevent uncontained rotor failure. It targets particular part numbers and serial numbers and prescribes removal/inspection timing and an authorised inspection provider. There is no evidence in the text provided that the AD has been broadened beyond that manufacturing‑defect remediation scope."},"complexity_factors":["Multiple engine sub‑variants listed in the Applicability section (around 20 variants across two groups).","Two distinct affected part numbers (P/N 3075772‑1 and 3060841‑1) with separate serial‑number tables in two Honeywell service/alert bulletins.","Dependence on external documents: Table 1 of two Honeywell Service Bulletins to identify affected serial numbers (cross‑reference dependency).","Conditional drawdown schedule with different CSN thresholds for two engine groups (4,200/4,300 vs 3,200/3,300) and a 100 cycles‑in‑service immediate window for high CSN discs (nested timing rules).","Mandatory use of a single, named repair station (Honeywell Phoenix, Cert. ZN3R030M) for the required inspection (restricts where compliance can occur).","A specific operational definition of “access” tied to a level of disassembly (removal of the HP turbine rotor assembly), which affects when removal is required. ","Cross‑reference to a related FAA AD and to Honeywell service material (adds layers for research and concurrent compliance)."],"plain_english_summary":"**What this instrument does (mechanically)**\n\n- Applies to Honeywell (formerly AlliedSignal/Garrett/AiResearch) TFE731 family turbofan engines listed under “Applicability” (multiple sub‑variants used on a wide range of business jets). (See “Applicability”.)\n\n- Requires removal from service of high‑pressure (HP) turbine rotor assemblies when those assemblies contain HP turbine rotor discs of specific part numbers and serial numbers identified in Honeywell service documents: P/N 3075772‑1 for the first group of engine models, and P/N 3060841‑1 for the second group. The affected serial numbers are listed in Table 1 of the Honeywell Service Bulletin(s) referenced in the AD. (See “Requirement” paragraphs 1–2 and the referenced Honeywell SBs.)\n\n- Sets mandatory timing (a “drawdown” schedule) for when the rotor assemblies must be removed, based on cycles‑since‑new (CSN):\n  - For the first engine group: discs with ≥4,200 CSN must be removed within 100 cycles‑in‑service; discs with <4,200 CSN must be removed at next access to the HP turbine but not later than 4,300 CSN. (Compliance 1a–1b.)\n  - For the second engine group: the analogous thresholds are 3,200 CSN (remove within 100 CIS) and a hard limit at 3,300 CSN for those with fewer than 3,200 CSN. (Compliance 2a–2b.)\n\n- Prohibits reinstallation of the affected HP turbine rotor discs unless they pass a specific inspection (a curvic root radius inspection) performed by Honeywell Engines, Systems and Services, Phoenix, Arizona, Certificate Repair Station No. ZN3R030M. (Requirement 3.)\n\n- Defines “access” to the HP turbine rotor discs as removal of the HP turbine rotor assembly from the engine (so the removal requirement is triggered only when that level of disassembly occurs). (Requirement 3, Note about access.)\n\n- The regulator (Civil Aviation Safety Authority) set an effective date for the AD and enforces compliance. (See “Compliance” and effective date.)\n\n**Why the rule exists (stated rationale) and what it aims to prevent**\n\n- The manufacturer reported that some HP turbine rotor discs were manufactured with improperly machined radii at the root of the forward and aft curvic teeth. The AD’s stated purpose is to prevent an uncontained failure of the HP turbine rotor assembly (parts departing the engine) which could damage the aircraft. (See “Background”.)\n\n**Who is directly affected**\n\n- Aircraft/operators that use the listed TFE731 engine variants and that have engines containing the identified P/Ns and serial numbers. Primary obligations fall on certificate holders/operators to remove the assemblies per the timetable, and to ensure discs are inspected and cleared before reinstallation. The specified Honeywell Phoenix repair station is the only authorised facility for the required inspection under this AD. (Requirements 1–3; Compliance 1–3.)\n\n**Who pays and who decides**\n\n- Operators/owners pay the direct costs: engine removal or access, shipping, the inspection fee, repair or replacement if discs fail inspection, and aircraft downtime. Honeywell (the manufacturer) performs the mandated inspection at its Phoenix repair station; CASA (the regulator) mandates and enforces the requirement. The AD references Honeywell service bulletins as the source of serial‑number identification.\n\n**Practical effects, trade‑offs and implementation considerations**\n\n- Compliance creates operational downtime and logistics costs: removing the HP rotor assembly, shipping discs to the specified repair station, and potentially fitting replacement parts. The AD limits where the mandatory inspection may be done (Honeywell Phoenix, cert. ZN3R030M), which concentrates demand and could create scheduling delays.\n\n- Incentives for operators: to avoid extended downtime they may choose to replace suspect discs with known good spares (if available) rather than wait for inspection results, increasing parts demand and short‑term costs for spares inventories.\n\n- Compliance monitoring requires accurate tracking of cycles‑since‑new (CSN) and recordkeeping to determine which removal trigger applies (the 100‑cycle window vs removal at next access). The AD clarifies what “access” means (removal of the HP rotor assembly), reducing ambiguity about when the less urgent removal option applies.\n\n- The AD relies on manufacturer‑supplied serial‑number lists (Table 1 of Honeywell SBs) to define affected items; operators must consult those SBs to identify affected discs. The AD also cross‑references a related FAA AD. (Requirement references and notes.)\n\n**Net mechanics in one sentence**\n\nOperators of affected TFE731 engines must remove certain HP turbine rotor assemblies containing specifically identified disc part numbers/serial numbers within specified CSN windows, and may only reinstall discs that pass a curvic root radius inspection performed by the named Honeywell Phoenix repair station, to address manufacturing defects in the curvic tooth radii and reduce the risk of uncontained failure."},"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This AD maintains its original scope as a targeted safety directive addressing a specific manufacturing defect in identified engine models. The applicability section lists affected aircraft types comprehensively but this represents standard aviation safety practice for ensuring operators can identify affected fleets, not scope creep."},"complexity_factors":["Multiple engine model variants with different part numbers and compliance schedules (two distinct drawdown schedules based on engine series)","Cross-reference to two separate Honeywell Service Bulletins for serial number identification (SB TFE731-72-3720 and Alert SB TFE731-A72-5185)","Conditional compliance based on accumulated flight cycles (CSN - Cycles Since New) with tiered deadlines","Reference to external FAA AD 2008-02-19 for harmonisation context","Specific repair station certification requirement (Honeywell Phoenix, Certificate No. ZN3R030M) for reinstallation eligibility","Technical aviation terminology requiring domain knowledge (curvic couplings, CSN, CIS, uncontained failure)"],"plain_english_summary":"CASA requires operators of Honeywell TFE731 engines on business jets to remove certain high‑pressure turbine rotor discs because a machining defect in the curvic coupling could cause catastrophic uncontained disc failure. Removal deadlines are cycle‑based (short near‑term windows for high‑time parts, routine removal before specified cycle limits for others).\n\nRemoved discs must be inspected and cleared by Honeywell before reinstallation. The AD prevents potential engine explosions and aligns with a corresponding FAA directive."}},"importantCases":[],"_links":{"self":"/api/acts/ad-tfe731-35-high-pressure-turbine-rotor-discs-curvic-couplings","history":"/api/acts/ad-tfe731-35-high-pressure-turbine-rotor-discs-curvic-couplings/history","analysis":"/api/acts/ad-tfe731-35-high-pressure-turbine-rotor-discs-curvic-couplings/analysis","conflicts":"/api/acts/ad-tfe731-35-high-pressure-turbine-rotor-discs-curvic-couplings/conflicts","importantCases":"/api/acts/ad-tfe731-35-high-pressure-turbine-rotor-discs-curvic-couplings/important-cases","documents":"/api/acts/ad-tfe731-35-high-pressure-turbine-rotor-discs-curvic-couplings/documents"}}