{"id":"F2006B02253","name":"AD/AL 250/4 - Sixth Stage Compressor Blades - Modification","slug":"ad-al-250-4-sixth-stage-compressor-blades-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41483,"registerId":"commonwealth-F2006B02253-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AL 250/4 - Sixth Stage Compressor Blades - Modification","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 250/4 Sixth Stage Compressor Blades - Modification 6/68\n\nApplicability: All model 250-C18 fitted with compressor assemblies prior to S/N CAC 20873 and Model 250-C18A fitted with compressor assemblies prior to S/N CAC 20188.\n\n \n\nDocument: Allison CEB No. 250 CEB-48. Compliance: Before further flight after 19 June 1968.\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, targeted safety directive addressing a specific mechanical defect in specific engine models. It has not expanded beyond its original purpose of mandating a compressor blade modification."},"complexity_factors":["Very short document (approximately 150 words)","Only 2 defined applicability criteria (engine models and serial number cutoffs)","Single compliance requirement with clear deadline","No cross-references to other legislation or regulations beyond the parent Civil Aviation Regulations 1998","No conditional logic, exceptions, or nested provisions","Refers to external technical document (Allison CEB) rather than reproducing complex technical specifications inline"],"plain_english_summary":"**What this is:** This is an **Airworthiness Directive (AD)** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) that requires specific repairs or modifications to aircraft engines.\n\n**What it does:** It orders owners and operators of certain **Allison 250 series turbine engines** to modify the **sixth stage compressor blades** (a set of rotating fan blades deep inside the engine that compress air for combustion).\n\n**Who it affects:** \n- **Model 250-C18 engines** with compressor assemblies made before serial number CAC 20873\n- **Model 250-C18A engines** with compressor assemblies made before serial number CAC 20188\n\nThese are typically found in light helicopters and small turboprop aircraft.\n\n**What must be done:** Operators must follow the instructions in **Allison CEB No. 250 CEB-48** (a manufacturer's service bulletin) and complete the modification **before the aircraft flies again after 19 June 1968**.\n\n**Why it matters:** Compressor blade failures can cause catastrophic engine damage and crashes. This directive addresses a known defect in early production compressor assemblies to prevent in-flight engine failures."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The supplied AD specifies a narrowly targeted mandatory modification for particular engine models and serial-numbered compressor assemblies and sets a firm compliance deadline. The text contains no information indicating a change from an earlier or original scope; it states the applicability and the required action as a single, focused directive."},"complexity_factors":["Narrow technical scope limited to a single component (sixth-stage compressor blades) and two engine models","Applicability determined by specific compressor assembly serial numbers (S/N CAC 20873 and CAC 20188), requiring accurate parts/records tracking","Mandated compliance timing: \"Before further flight\" after a specific date, giving no operational flexibility","Reference to an external manufacturer document (Allison CEB No. 250 CEB-48) for technical implementation, with required cross-checking of that document","Minimal procedural detail in the AD text itself (no cost, no alternate compliance path, no inspection protocol stated), increasing reliance on the referenced CEB and maintenance judgement"],"plain_english_summary":"This directive requires owners/operators to modify the sixth-stage compressor blades on specified Allison 250-C18 and 250-C18A engines (those with compressor assemblies before listed serial numbers) using Allison CEB No. 250 CEB-48.  \n\nThe work must be done before the next flight after 19 June 1968; operators bear the cost and downtime. It’s a mandatory airworthiness fix; no operational discretion to defer."}},"importantCases":[],"_links":{"self":"/api/acts/ad-al-250-4-sixth-stage-compressor-blades-modification","history":"/api/acts/ad-al-250-4-sixth-stage-compressor-blades-modification/history","analysis":"/api/acts/ad-al-250-4-sixth-stage-compressor-blades-modification/analysis","conflicts":"/api/acts/ad-al-250-4-sixth-stage-compressor-blades-modification/conflicts","importantCases":"/api/acts/ad-al-250-4-sixth-stage-compressor-blades-modification/important-cases","documents":"/api/acts/ad-al-250-4-sixth-stage-compressor-blades-modification/documents"}}