{"id":"F2006B02251","name":"AD/AL 250/37 - Third Stage Turbine Wheel - Replacement","slug":"ad-al-250-37-third-stage-turbine-wheel-replacement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41481,"registerId":"commonwealth-F2006B02251-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AL 250/37 - Third Stage Turbine Wheel - 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)  Allison Turbine Engines - 250 Series\n\n \n\nAD/AL 250/37 Third Stage Turbine Wheel - Replacement 9/79\n\nApplicability: All 250-C28 series engines fitted with third stage turbine wheel P/No. 6898553 or 6898773.\n\n \n\nRequirement: Remove affected Part Number Turbines from service.\n\n \n\nNote: FAA Emergency AD Dated 19 July 1979 refers.\n\n \n\nCompliance: 1. For turbines with more than 300 hours’ time in service - Within 25 hours’ time in service from 9 August 1979.\n\n \n\n2. For turbines with less than 300 hours’ time in service - Before reaching 325 hours’ time in service.\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, time-bound safety directive from 1979 addressing a specific mechanical defect. It has not expanded beyond its original narrow scope of replacing specific turbine wheels in specific engines."},"complexity_factors":["Single, specific mechanical defect addressed","Only two part numbers affected","Simple binary compliance structure based on flight hours (over/under 300 hours)","No defined terms section","No cross-references to other legislation (only a note about related FAA directive)","Straightforward applicability clause","Single requirement with clear deadline structure"],"plain_english_summary":"**What this is:** This is an Airworthiness Directive (AD) — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). Think of it like a factory recall for aircraft engines, but legally enforceable.\n\n**What it does:** It orders the immediate replacement of specific third-stage turbine wheels in Allison 250-C28 series engines. These are helicopter engines (commonly used in models like the Bell 206 JetRanger). The affected parts are identified by part numbers 6898553 and 6898773.\n\n**Who it affects:** Anyone operating aircraft with these specific Allison 250-C28 engines — typically helicopter operators, charter companies, emergency services, and private owners.\n\n**The safety issue:** The directive doesn't spell out the exact defect, but the \"Emergency\" classification and the tight compliance deadlines (25 flight hours or before 325 total hours) suggest a critical failure risk — likely catastrophic turbine wheel failure that could cause engine destruction and potential crash.\n\n**What operators must do:**\n- **High-time engines** (over 300 hours): Replace the turbine wheel within 25 flight hours of 9 August 1979\n- **Low-time engines** (under 300 hours): Replace the turbine wheel before the engine reaches 325 total flight hours\n\n**Why it matters:** This prevents potentially fatal engine failures. The reference to the FAA Emergency AD from July 1979 shows this was part of an urgent international response to a discovered defect. Non-compliance grounds the aircraft — it's illegal to fly until fixed."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The directive's scope is confined to removal and replacement of third-stage turbine wheels with part numbers 6898553 or 6898773 on Allison 250-C28 series engines (Applicability; Requirement). There is no text in the instrument that expands or narrows that applicability beyond the stated parts and engine series; therefore the scope as written matches the instrument's explicit operative text."},"complexity_factors":["Narrow technical scope: applies only to Allison 250-C28 engines with two specific part numbers (Applicability).","Single mandated action: removal/replacement of the identified turbine wheels (Requirement).","Simple, time-based compliance windows with only two branches (>300 hours and <300 hours) (Compliance).","No discretionary remedial options or complex compliance procedures specified; straight replacement mandate (Requirement; Compliance).","Reference to external FAA Emergency AD increases cross-jurisdictional traceability but does not add procedural complexity within this instrument (Note)."],"plain_english_summary":"### What this instrument does, simply\n\nThis Airworthiness Directive (AD) orders the removal and replacement of a specific third-stage turbine wheel fitted to certain Allison 250-C28 series engines. It applies only to turbine wheels with part numbers 6898553 or 6898773 (Applicability). The directive requires operators to take those turbine wheels out of service (Requirement) and sets two alternative compliance deadlines based on the wheel's recorded hours in service (Compliance):\n\n- If the turbine wheel already has more than 300 hours time in service: replace it within 25 hours time in service measured from 9 August 1979 (Compliance 1).\n- If the turbine wheel has less than 300 hours time in service: replace it before it reaches 325 hours time in service (Compliance 2).\n\nThe AD also refers to an FAA Emergency AD dated 19 July 1979 (Note).\n\n### Who is affected\n\n- Owners and operators of aircraft powered by Allison 250-C28 series engines that have a third-stage turbine wheel with part number 6898553 or 6898773 (Applicability).\n- Maintenance organisations and parts suppliers who will perform and supply the replacements.\n\n### Who pays and who decides\n\n- Aircraft owners/operators bear the direct costs: purchasing replacement parts, labour to remove and fit the new turbine wheel, and any aircraft downtime for the work (Requirement; Compliance).\n- The Civil Aviation Safety Authority set the mandatory timeline and requirement through this AD; operators may only decide on scheduling and sourcing within those mandatory time limits (Requirement; Compliance).\n\n### Behavioural effects and incentives\n\n- Operators must track the turbine wheel's time in service and schedule replacement within the specified windows. Failure to comply would leave the operator non‑compliant with the AD (Requirement; Compliance).\n- Maintenance providers may receive increased demand for parts and labour; operators face the incentive to source compliant replacement parts and complete the work promptly to meet the short deadlines (Requirement; Compliance).\n\n### Implementation trade-offs, costs and practical risks\n\n- Immediate costs: replacement parts and labour. These are concentrated on the owners/operators of affected engines (Requirement).\n- Operational costs: aircraft downtime while the replacement is carried out and possible rescheduling of flights or services to meet the short compliance windows (Compliance).\n- Supply risk: availability of replacement turbine wheels or qualified maintenance capacity may affect an operator's ability to comply within the specified hours (Compliance).\n- Administrative burden: operators must monitor and record time-in-service for affected turbine wheels to determine which compliance path applies and to meet the deadlines (Applicability; Compliance).\n- Discretion and enforcement: the AD sets mandatory actions and deadlines; it leaves little regulatory discretion to operators other than timing and sourcing within those deadlines (Requirement; Compliance).\n\n### Purpose claim and how it maps to costs and incentives\n\n- The AD refers to an FAA Emergency AD (Note), which the issuing authorities cite as the basis for the action. That referral indicates the directive is intended to address a safety concern identified by the FAA. The concrete mechanism is removal and replacement of the specified part numbers on the stated engines to eliminate the identified risk (Applicability; Requirement; Note).\n- The trade-off is immediate, concentrated cost and operational disruption for aircraft owners/operators versus the intended reduction in the risk associated with continuing to operate the specific turbine wheels (Requirement; Compliance)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-al-250-37-third-stage-turbine-wheel-replacement","history":"/api/acts/ad-al-250-37-third-stage-turbine-wheel-replacement/history","analysis":"/api/acts/ad-al-250-37-third-stage-turbine-wheel-replacement/analysis","conflicts":"/api/acts/ad-al-250-37-third-stage-turbine-wheel-replacement/conflicts","importantCases":"/api/acts/ad-al-250-37-third-stage-turbine-wheel-replacement/important-cases","documents":"/api/acts/ad-al-250-37-third-stage-turbine-wheel-replacement/documents"}}