{"id":"F2006B11212","name":"AD/LYC/91 - Crankshaft Removal/Inspection","slug":"ad-lyc-91-crankshaft-removal-inspection","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"repealed","isInForce":false,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56930,"registerId":"commonwealth-F2006B11212-current","compilationNumber":null,"startDate":"2026-04-02","status":"Repealed","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/LYC/91 - Crankshaft Removal/Inspection","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 106 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nLycoming Piston Engines\n\nAD/LYC/91 Crankshaft Removal/Inspection 10/92 DM\n\nApplicability: All Textron Lycoming piston engines that have been overhauled by or had the crankcase disassembled for major work by Arnhem Aircraft Engineering Pty Ltd under Certificate of Approval No. 4049 during the period 1 January 1990 to 6 August 1992.\n\nRequirement: 1. Remove the crankshaft assembly and dimensionally check the diameters of all bearing journals.\n\n    2. Crankshafts with any bearing journal diameter less than the STANDARD dimension listed in the relevant Textron Lycoming Engine Overhaul Manual are to be quarantined and the CAA local Airworthiness District Office notified.\n\n    3. Crankshafts with diameters for all bearing journals at the STANDARD dimension listed in the relevant Textron Lycoming Engine Overhaul Manual may be refitted to an engine.\n\nCompliance: For installed engines \\- Prior to the 31 August 1992.\n\nFor uninstalled engines \\- Before installation into aircraft.\n\nBackground: Four crankshaft assemblies repaired by the grinding of bearing journals on behalf of Arnhem Aircraft Engineering Pty Ltd have been found with grinding cracks, two of which failed in flight. Arnhem Aircraft Engineering Pty Ltd has been unable to satisfy the CAA (Australia) as to the location or number of crankshafts repaired by grinding on its behalf.","sortOrder":0}],"analysis":{"kimi_summary":{"_metrics":{"model":"kimi-k2.5","source":"moonshot-batch","completionTokens":2513},"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is the original issuance of the directive, establishing mandatory inspection requirements in response to identified airworthiness hazards. The scope remains precisely targeted at the specific maintenance history and defect pattern involving Arnhem Aircraft Engineering between January 1990 and August 1992."},"complexity_factors":["Single, clearly defined applicability criterion (specific maintenance organization and date range)","Straightforward two-step requirement (remove and measure, then quarantine or refit)","Binary compliance pathway (installed vs uninstalled engines)","Reference to external technical manual for dimensional standards","No nested exceptions, conditional clauses, or cross-references to other legislative provisions"],"plain_english_summary":"This urgent Airworthiness Directive requires owners/operators of Textron Lycoming piston engines overhauled by Arnhem Aircraft Engineering (Jan 1990–Aug 1992) to remove and inspect crankshafts for undersized bearing journals. Any undersized crankshaft must be quarantined and reported to the Civil Aviation Authority; only crankshafts meeting manufacturer dimensions may be reused.\n\nFor engines in aircraft the inspection must be done before 31 August 1992; spare engines must be inspected before installation. This prevents in‑flight crankshaft failures."}},"importantCases":[],"_links":{"self":"/api/acts/ad-lyc-91-crankshaft-removal-inspection","history":"/api/acts/ad-lyc-91-crankshaft-removal-inspection/history","analysis":"/api/acts/ad-lyc-91-crankshaft-removal-inspection/analysis","conflicts":"/api/acts/ad-lyc-91-crankshaft-removal-inspection/conflicts","importantCases":"/api/acts/ad-lyc-91-crankshaft-removal-inspection/important-cases","documents":"/api/acts/ad-lyc-91-crankshaft-removal-inspection/documents"}}