{"id":"F2006B02266","name":"AD/AL 250/54 Amdt 1 - Engine Turbine Assembly No. 8 Bearing U-Ring Installation","slug":"ad-al-250-54-amdt-1-engine-turbine-assembly-no-8-bearing-u-ring-installation","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41496,"registerId":"commonwealth-F2006B02266-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AL 250/54 Amdt 1 - Engine Turbine Assembly No. 8 Bearing U-Ring Installation","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 250/54\n\nAmdt 1\n\n\nEngine Turbine Assembly No. 8 Bearing U-Ring Installation\n\n\n5/84\n\n \n\nApplicability: Allison 250-C28B/C28C engines.\n\n \n\nDocument: Allison 250 C28B/C28C CEB-A-72-2082 Rev 1.\n\n \n\nNote: FAA AD Allison 83-01-04 AMDT. 39-4539 refers.\n\n \n\nCompliance: In accordance with the Requirement Documents.\n\n \n\nBackground: This have been instances of an air leak occurring into the No. 8 bearing sump, forcing oil through the No. 8 bearing labyrinth seal onto the No. 1 turbine wheel, resulting in oil fires and damage to first stage turbine wheels. This Directive is raised in issue to ensure compliance with Revision 1 of the document which is a complete revision replacing the original.\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":{"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"The Directive explicitly requires compliance with Revision 1 of the Allison document and states that Revision 1 is a complete revision replacing the original (\"This Directive is raised in issue to ensure compliance with Revision 1 of the document which is a complete revision replacing the original\"). That language indicates the technical scope has been changed from the original document and that the AD is enforcing the revised, comprehensive instructions rather than the earlier version."},"complexity_factors":["Safety‑critical technical subject matter (turbine bearing U‑ring and labyrinth seal interactions).","Mandatory cross‑reference to an external Requirement Document (CEB-A-72-2082 Rev 1) that contains the operative technical instructions rather than including them in the AD text (\"Document: Allison 250 C28B/C28C CEB-A-72-2082 Rev 1\"; \"Compliance: In accordance with the Requirement Documents\").","Applicability limited to specific engine models, requiring operators to identify affected engines (\"Applicability: Allison 250-C28B/C28C engines\").","Interplay with overseas regulator action (FAA AD reference), creating cross‑jurisdictional alignment considerations (\"Note: FAA AD Allison 83-01-04 AMDT. 39-4539 refers\").","Safety consequence described (oil leaks can produce fires and damage turbine wheels), meaning compliance has high operational importance and low tolerance for error (\"Background: ...resulting in oil fires and damage to first stage turbine wheels\").","Lack of procedural detail in the AD itself increases administrative load to obtain and review the Requirement Document and to plan compliance actions (implementation dependency).","Potential supply/maintenance logistics (parts, qualified labour, and aircraft downtime) implied by a required mechanical installation but not detailed in the instrument."],"plain_english_summary":"This AD mandates that operators and maintenance organisations for Allison 250‑C28B/C28C engines follow Allison CEB‑A‑72‑2082 Rev 1 for No. 8 bearing U‑ring installation. It aims to stop air leaks into the No. 8 bearing sump that can force oil onto the No. 1 turbine wheel, causing oil fires and first‑stage turbine damage. Practical effect: technical requirements sit in the Revision 1 document and compliance costs, scheduling and execution fall to operators and their maintenance providers."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a narrow, targeted safety directive addressing a specific mechanical defect in specific engine models. It has not expanded beyond its original purpose of preventing oil leaks and fires in the No. 8 bearing assembly."},"complexity_factors":["Very short document (approximately 200 words)","Only 2 defined applicability criteria (specific engine models)","Single cross-reference to FAA AD 83-01-04","No nested conditional logic or exceptions","Straightforward compliance requirement (follow the referenced document)","Single technical issue addressed with direct causal chain"],"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 maintenance action on aircraft engines.\n\n**What it does:** It orders owners and operators of **Allison 250-C28B and 250-C28C turbine engines** to follow a specific technical document (Allison CEB-A-72-2082 Revision 1) when installing the U-ring seal on the No. 8 bearing in the engine's turbine assembly.\n\n**Why it matters:** There have been cases where air leaked into the No. 8 bearing sump (the chamber that holds lubricating oil). This forced oil past the labyrinth seal (a type of seal with a complex path that blocks leakage) onto the hot No. 1 turbine wheel, causing **oil fires and damage to turbine wheels**. This directive prevents engine fires and potential catastrophic failure by ensuring mechanics use the updated, corrected installation procedure.\n\n**Who must comply:** Anyone operating or maintaining aircraft with these specific Allison 250 series engines — typically used in helicopters and light aircraft.\n\n**Key point:** This is an amended directive (Amendment 1) that completely replaces the original version with a full technical revision of the required procedure."}},"importantCases":[],"_links":{"self":"/api/acts/ad-al-250-54-amdt-1-engine-turbine-assembly-no-8-bearing-u-ring-installation","history":"/api/acts/ad-al-250-54-amdt-1-engine-turbine-assembly-no-8-bearing-u-ring-installation/history","analysis":"/api/acts/ad-al-250-54-amdt-1-engine-turbine-assembly-no-8-bearing-u-ring-installation/analysis","conflicts":"/api/acts/ad-al-250-54-amdt-1-engine-turbine-assembly-no-8-bearing-u-ring-installation/conflicts","importantCases":"/api/acts/ad-al-250-54-amdt-1-engine-turbine-assembly-no-8-bearing-u-ring-installation/important-cases","documents":"/api/acts/ad-al-250-54-amdt-1-engine-turbine-assembly-no-8-bearing-u-ring-installation/documents"}}