{"id":"F2006L01353","name":"AD/AL501/5 - Third and Fourth Stage Turbine Wheels","slug":"ad-al501-5-third-and-fourth-stage-turbine-wheels","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":58881,"registerId":"commonwealth-F2006L01353-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Rolls Royce (Allison) Turbine Engines - ","sectionType":"division","heading":"Rolls Royce (Allison) Turbine Engines - AL501 Series","content":"### Rolls Royce (Allison) Turbine Engines - AL501 Series\n\n| AD/AL501/5 | Third and Fourth Stage Turbine Wheels | 6/2006 |\n| ---------- | ------------------------------------- | ------ |\n\n| Applicability: | Rolls Royce (formerly DETROIT DIESEL ALLISON) Model 501-D13/501-D13A/501-D13D/50l-D13E, and 501-D13H Engines equipped with third stage turbine wheel part numbers (P/N’s) 6788833, 6842143, 6841223, and 6846553 or fourth stage turbine wheel P/N’s 6738424 and 6843014.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n| Requirement:   | 1. Unless previously accomplished, remove and classify all third and fourth stage turbine wheels with unknown carbide precipitation classifications in accordance with the procedures specified in Detroit Diesel Allison Commercial Overhaul Information Letter No. 349 Rev. 1 or later FAA approved revision.2. Wheels both newly and previously classified with carbide precipitation classifications of “Heavy” must be removed from service in accordance with the maximum life limits specified in Compliance 2.3. Wheels both newly and previously classified with carbide precipitation classifications of “Medium Heavy” must be removed from service in accordance with the maximum life limits specified in Compliance 3.Wheels of all other classifications may be returned to service and operated in accordance with the existing hourly life limits.Note: FAA AD 78-09-09 Amendment 39-3207 refers. |\n| Compliance:    | 1. Within 30 days after the effective date of this AD.2. For wheels of “Heavy” and unknown carbide precipitation classification which exceed 8000 total cycles upon the effective date of this AD compliance is required within 300 cycles; orFor wheels of “Heavy” and unknown carbide precipitation classification which do not exceed 8000 total cycles upon the effective date of this AD, compliance is required prior to reaching 8300 total cycles.3. For wheels of “Medium Heavy” carbide precipitation classification which exceed 16,000 total cycles upon effective date of this AD, compliance is required within 200 cycles; or                                                                                                                                                                                                                                                                       |\n\n|             | For wheels of “Medium Heavy” carbide precipitation classification which have from 14,000 to 16,000 total cycles upon the effective date of this AD, compliance is required within the next 400 cycles or prior to exceeding 16,200 cycles whichever occurs first; orFor wheels of “Medium Heavy” carbide precipitation classification which have from 10,500 to 14,000 total cycles upon the effective date of this AD, compliance is required within the next 1000 cycles or prior to exceeding 14,400 total cycles whichever occurs first; orFor wheels of “Medium Heavy” carbide precipitation classification which have from 8000 to 10,500 total cycles on the effective date of this AD, compliance is required within the next 2000 cycles or prior to exceeding 11,500 total cycles whichever occurs first; orFor wheels of “Medium Heavy” carbide precipitation classification which have from 7000 to 8000 total cycles on the effective date of this AD, compliance is required prior to exceeding 10,000 cycles; orFor wheels of “Medium Heavy” carbide precipitation classification which do not exceed 7000 total cycles upon the effective date of this AD, compliance is required prior to exceeding 8000 cycles.For purposes of this airworthiness directive a cycle is defined as one takeoff. |\n| ----------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n|             | This Airworthiness Directive becomes effective on 8 June 2006.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |\n| Background: | The requirements of this AD are to preclude failure of the 3rd or 4th Stage turbine wheels based upon the level of carbide precipitation. It has been determined that the level of carbide precipitation may affect the projected safe life of the turbine wheel.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |\n\n![](image.001.png)  \nJames Coyne  \nDelegate of the Civil Aviation Safety Authority\n\n28 April 2006","sortOrder":0},{"sectionNumber":"AD/AL501/5","sectionType":"part","heading":"AD/AL501/5","content":"## AD/AL501/5","sortOrder":1},{"sectionNumber":"Third and Fourth Stage Turbine Wheels","sectionType":"part","heading":"Third and Fourth Stage Turbine Wheels","content":"## Third and Fourth Stage Turbine Wheels","sortOrder":2},{"sectionNumber":"6/2006","sectionType":"part","heading":"6/2006","content":"## 6/2006","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":7,"scope_assessment":{"changed":false,"description":"Scope is confined to the specified AL501 engine models and enumerated third- and fourth-stage turbine wheel part numbers and prescribes classification plus retirement based on carbide precipitation and total cycles. The instrument does not, on its face, expand to other engines or parts beyond those listed (Applicability; Requirement)."},"complexity_factors":["Technical metallurgical classification requirement (carbide precipitation levels) that determines different mandatory actions (Requirement).","Multiple, tiered life-limit thresholds keyed to both classification and a wheel's existing total cycles, creating many conditional deadlines (Compliance).","Short compliance windows (e.g. 30 days to classify; various cycle-count windows down to 100–300 cycles) increasing operational scheduling pressure (Compliance).","Narrow applicability limited to specific engine models and six part numbers, requiring accurate parts identification and paperwork (Applicability).","Cross-reference to an external service document (Detroit Diesel Allison Commercial Overhaul Information Letter No.349 Rev.1 or later FAA-approved revision) adds dependency on another technical source (Requirement).","Definition of ‘cycle’ as one takeoff imposes tracking requirements on operators/logbooks and affects lifecycle accounting (Compliance).","Reference to an earlier FAA AD (FAA AD 78-09-09) introduces potential legacy compliance history considerations (Requirement/Note)."],"plain_english_summary":"Requires operators of specified Rolls‑Royce (Allison) AL501-series engines fitted with the listed third- and fourth-stage turbine wheels to remove and classify those wheels for carbide precipitation and to retire wheels when their classification and accumulated cycles hit prescribed life limits. (Applicability; Requirement)\n\nThe stated purpose is to prevent wheel failure by imposing shorter lives for wheels classified “Heavy” or “Medium Heavy.” Operators must inspect/replace wheels to tight deadlines and cycle-counts (a cycle = one takeoff) and follow Detroit Diesel Allison Overhaul Letter No.349 or later FAA‑approved revision. (Compliance; Background)"},"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 focused scope on its original safety purpose — preventing turbine wheel failures due to carbide precipitation in specific Allison 501-D13 engine variants. The compliance structure, while elaborate, remains tightly bound to the original technical finding about metallurgical degradation. No mission creep or expansion beyond the specific part numbers and failure mode identified in the background."},"complexity_factors":["Multiple nested conditional compliance deadlines based on both carbide classification AND current cycle count (7 distinct compliance pathways for 'Medium Heavy' classification alone)","Cross-reference to external technical document (Detroit Diesel Allison Commercial Overhaul Information Letter No. 349 Rev. 1) without reproducing its contents","Reference to US FAA AD 78-09-09 Amendment 39-3207, creating transnational regulatory dependency","Precise part number applicability requiring technical cross-checking (6 specific P/N's across two wheel stages)","Defined term 'cycle' provided, but 'carbide precipitation classification' relies on external technical expertise","Dual classification system (newly classified vs previously classified wheels) with identical treatment, creating redundant conditional structure"],"plain_english_summary":"This AD requires operators of certain Rolls‑Royce (former Detroit Diesel Allison) 501‑D13 turbine engines to inspect and, if necessary, remove third‑ and fourth‑stage turbine wheels that show medium‑heavy or heavy carbide precipitation. It targets wheels whose carbide condition is unknown or degraded.\n\nIt matters because carbide precipitation weakens these high‑speed components; failure can cause catastrophic engine damage and risk to the aircraft, so weakened wheels must be retired before they reach dangerous life limits."}},"importantCases":[],"_links":{"self":"/api/acts/ad-al501-5-third-and-fourth-stage-turbine-wheels","history":"/api/acts/ad-al501-5-third-and-fourth-stage-turbine-wheels/history","analysis":"/api/acts/ad-al501-5-third-and-fourth-stage-turbine-wheels/analysis","conflicts":"/api/acts/ad-al501-5-third-and-fourth-stage-turbine-wheels/conflicts","importantCases":"/api/acts/ad-al501-5-third-and-fourth-stage-turbine-wheels/important-cases","documents":"/api/acts/ad-al501-5-third-and-fourth-stage-turbine-wheels/documents"}}