{"id":"F2006L03493","name":"AD/AL 250/90 - Turbine Wheel Event Thresholds and Maximum Overspeed Transients","slug":"ad-al-250-90-turbine-wheel-event-thresholds-and-maximum-overspeed-transients","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":61013,"registerId":"commonwealth-F2006L03493-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Allison Turbine Engines - 250 Series","sectionType":"division","heading":"Allison Turbine Engines - 250 Series","content":"### Allison Turbine Engines - 250 Series\n\n| AD/AL 250/90 | Turbine Wheel Event Thresholds andMaximum Overspeed Transients | 12/2006 |\n| ------------ | -------------------------------------------------------------- | ------- |\n\n| Applicability: | Rolls-Royce Corporation (RRC) models 250- C30, -C30G, -C30G/2, -C30M, -C30P, -C30R, -C30R/1, -C30R/3, -C30R/ 3M, -C30S, -C30U, -C40B, -C47B, and -C47M turboshaft engines, with a third-stage turbine wheel, part number (P/N) 6898663 or P/N 23065843 installed, or a fourth-stage turbine wheel, P/N 6892764 or P/N 23066744, installed.Note 1: These engines are installed on, but not limited to, Bell 206L-3, Bell 206L-4, Bell 230, Bell 407, Bell 430, MDHI 369F, MDHI 369FF, MDHI 600N, and Sikorsky S-76A helicopters.                                                                                                                                                                                                                                                                                                                                                                    |\n| -------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | 1. Record each time the third- and fourth-stage turbine wheels enter into the speed range between \"Event Threshold\" and \"Maximum Overspeed Transient\". Use paragraph 2.A. through 2.A.(5) of the Accomplishment Instructions and the applicable Figures 1 through 5 of RRC Alert Commercial Engine Bulletins (CEBs) No. CEB A-72-3272, No. CEB A-72-5048, and No. CEB A-72-6054 (combined in one document), all Revision 2, dated 27 June 2006 to determine the speed range.2. Remove and retire any third-stage turbine wheel or fourth- stage turbine wheel.Note 2: The retirement criteria in this AD are in addition to the existing third- and fourth-stage turbine wheel hour and cycle life limits. Wheels must be retired when they exceed any published life limit (transient speed excursions, hours, or cycles).Note 3: FAA AD 2006-20-07 Amdt 39-14776 dated 20 September 2006 refers. |\n| Compliance:    | 1. Within 30 days after the effective date of this AD.2. Before further flight after the sixth time the wheel enters into the speed range between \"Event Threshold\" and \"Maximum Overspeed Transient\".                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |\n|                | This Airworthiness Directive becomes effective on 23 November 2006.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |\n\n| Background: | This AD results from analysis by RRC of failures of third-stage turbine wheels. The issuing of this AD is to prevent loss of power possible engine shutdown, or uncontained failure. |\n| ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n\n![](image.001.png)  \nJames Coyne  \nDelegate of the Civil Aviation Safety Authority\n\n13 October 2006","sortOrder":0},{"sectionNumber":"AD/AL 250/90","sectionType":"part","heading":"AD/AL 250/90","content":"## AD/AL 250/90","sortOrder":1},{"sectionNumber":"Turbine Wheel Event Thresholds andMaximu","sectionType":"part","heading":"Turbine Wheel Event Thresholds andMaximum Overspeed Transients","content":"## Turbine Wheel Event Thresholds and  \nMaximum Overspeed Transients","sortOrder":2},{"sectionNumber":"12/2006","sectionType":"part","heading":"12/2006","content":"## 12/2006","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":false,"description":"The AD's scope aligns with its stated safety purpose: it applies to the listed RRC 250 engine models with the specified third‑ and fourth‑stage turbine wheel part numbers and imposes event logging plus retirement triggers. It does not expand requirements beyond those engines/wheels or beyond retirement in addition to existing life limits."},"complexity_factors":["Dependence on external engineering guidance: requires using paragraph 2.A–2.A.(5) and Figures 1–5 of three combined RRC Alert CEBs (Revision 2, 27 June 2006) to determine the speed range.","Multiple technical thresholds: distinguishes between 'Event Threshold' and 'Maximum Overspeed Transient' for third‑ and fourth‑stage wheels, requiring precise speed interpretation.","Applicability breadth: covers many RRC 250 model variants and two specific part‑numbered third‑ and fourth‑stage turbine wheels across multiple helicopter types.","Dual compliance triggers and deadlines: initial action within 30 days and mandatory retirement before further flight after a sixth recorded event, adding operational scheduling constraints.","Interaction with existing limits: retirement rules are explicitly additional to published hour/cycle life and transient limits, creating layered compliance obligations.","Recordkeeping burden: operators must log every qualifying speed excursion and track cumulative events to determine retirement timing.","Safety‑critical enforcement: noncompliance risks immediate flight‑safety consequences, increasing regulatory scrutiny and potential grounded time.","Reference to external regulator action: links to FAA AD 2006‑20‑07, indicating cross‑jurisdictional regulatory alignment and potential for harmonised compliance expectations."],"plain_english_summary":"This Airworthiness Directive requires operators of specified Rolls‑Royce 250‑series turboshaft engines with certain third‑ or fourth‑stage turbine wheels to record each time a wheel reaches the defined speed range between an \"Event Threshold\" and a \"Maximum Overspeed Transient\" (using RRC Alert CEBs) and to remove and retire wheels when retirement triggers occur. It affects helicopter operators and maintenance organisations who must change inspection and replacement practices; the regulator sets two compliance deadlines (30 days, and before flight after the sixth event) and enforces retirement in addition to existing life limits."},"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 narrow safety purpose: addressing specific turbine wheel failures in Rolls-Royce 250-series engines. The scope remains tightly focused on the identified safety risk without expansion into broader operational or maintenance requirements."},"complexity_factors":["Multiple cross-referenced technical documents: Requires consultation of three separate Rolls-Royce Commercial Engine Bulletins (CEBs A-72-3272, A-72-5048, and A-72-6054) to determine actual speed thresholds","Nested applicability criteria: Applies to 13 specific engine models with 4 specific part numbers across 2 different turbine wheel stages (third and fourth)","Dual compliance triggers: Different deadlines for starting record-keeping (30 days) versus part retirement (immediate upon 6th event)","Cumulative counting requirement: Operators must track and count transient speed events over the life of the part, requiring ongoing record maintenance","Layered life limits: Retirement criteria operate alongside existing hour and cycle limits, creating three separate retirement triggers (transients, hours, cycles)"],"plain_english_summary":"This CASA Airworthiness Directive requires operators of helicopters with specified Rolls‑Royce 250-series engines to record each time certain third‑stage turbine wheels overspeed into a defined dangerous range. After six such events the wheel must be removed from service and permanently retired.\n\nIt targets operators and maintenance crews for Bell 206/407, Sikorsky S‑76A and similar types to prevent in‑flight power loss or uncontained engine failures; tracking must begin within 30 days of 23 Nov 2006."}},"importantCases":[],"_links":{"self":"/api/acts/ad-al-250-90-turbine-wheel-event-thresholds-and-maximum-overspeed-transients","history":"/api/acts/ad-al-250-90-turbine-wheel-event-thresholds-and-maximum-overspeed-transients/history","analysis":"/api/acts/ad-al-250-90-turbine-wheel-event-thresholds-and-maximum-overspeed-transients/analysis","conflicts":"/api/acts/ad-al-250-90-turbine-wheel-event-thresholds-and-maximum-overspeed-transients/conflicts","importantCases":"/api/acts/ad-al-250-90-turbine-wheel-event-thresholds-and-maximum-overspeed-transients/important-cases","documents":"/api/acts/ad-al-250-90-turbine-wheel-event-thresholds-and-maximum-overspeed-transients/documents"}}