{"id":"F2006B11412","name":"AD/OM-P/4 - Piston Pin Circlip - Replacement and Installation Procedure","slug":"ad-om-p-4-piston-pin-circlip-replacement-and-installation-procedure","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":57318,"registerId":"commonwealth-F2006B11412-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/OM-P/4 - Piston Pin Circlip - Replacement and Installation Procedure","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)  Omnipol Piston Engines\n\n \n\nAD/OM-P/4 Piston Pin Circlip - Replacement NK\n\nand Installation Procedure\n\nApplicability: Walter M4-111, M6-111, M332 and M337 engines.\n\n \n\nRequirement:  1. Piston pin circlips may be used only once, and shall be replaced with a new circlip after each removal from the piston groove, irrespective of the length of the time in service.\n\n \n\n2. The dimensional checks of new circlips and procedures for removal, gap positioning and installation of circlips specified in Omnipol SBs Nos. M4-111/29, M6-111/27, M332/55 and M337/50 shall be observed, using a circlip driver similar in principle to driver P/N Z 2-01503-01.\n\n \n\nCompliance: At each removal of circlip after 30 September 1974.\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\n \n\n \n\n \n\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The instrument itself specifies its applicability (Walter M4-111, M6-111, M332 and M337 engines) and prescribes the single-use rule plus procedural requirements. The text contains no indication that the scope has changed from an earlier or different intent; the directive is narrowly targeted to the listed engine models and to the replacement/installation practices set out in the named Service Bulletins (Applicability; Requirement 1; Requirement 2)."},"complexity_factors":["Narrow technical scope limited to four engine models (Applicability)","Single clear mandatory rule (single-use circlip) reduces legal ambiguity (Requirement 1)","Cross-reference to multiple Omnipol Service Bulletins for procedural detail increases operational complexity (Requirement 2)","Specific tooling requirement (driver similar to P/N Z 2-01503-01) creates a small procurement/compatibility task (Requirement 2)","Compliance timing tied to a historical date phrased as 'after 30 September 1974' introduces potential record/interpretation issues for legacy records (Compliance)","No enforcement or inspection mechanism described in the text increases uncertainty about administrative oversight"],"plain_english_summary":"This instrument requires owners, operators and maintenance organisations of Walter M4‑111, M6‑111, M332 and M337 piston engines to treat piston‑pin circlips as single‑use: any removed circlip must be replaced. It also mandates dimensional checks and removal/installation procedures set out in named Omnipol service bulletins and use of a circlip driver of the specified principle. Practical effects: recurring parts, labour and tooling costs and standardized installation to protect circlip integrity."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope: regulating the replacement and installation of piston pin circlips in specific Walter/Omnipol engine models. There is no evidence of scope creep or expansion beyond this specific maintenance safety issue."},"complexity_factors":["Very short document (under 200 words)","Only 2 substantive requirements with no sub-paragraphs or nested conditions","No defined terms section — all terminology is standard aviation maintenance language","Single cross-reference to manufacturer service bulletins (SBs) without complex integration","No exceptions, exemptions, or conditional logic","Clear, unambiguous compliance date (30 September 1974)"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety rule issued by Australia's Civil Aviation Safety Authority (CASA) that aircraft owners and mechanics must follow.\n\n**What it does:**\nThis directive sets strict rules for a specific small but critical engine part called a **piston pin circlip** (a metal ring that holds the piston pin in place inside aircraft engines made by Walter/Omnipol).\n\n**Key requirements:**\n- **Single-use only:** Once a circlip is removed from the engine, it cannot be reused — you must install a brand new one, even if the old one looks fine.\n- **Specific procedures:** Mechanics must follow exact instructions from the manufacturer's service bulletins when removing, checking, and installing these circlips.\n- **Special tool required:** Installation must use a specific type of circlip driver tool (similar to part number Z 2-01503-01).\n\n**Who it affects:**\nAnyone operating or maintaining aircraft with Walter M4-111, M6-111, M332, or M337 piston engines.\n\n**Why it matters:**\nCirclip failure can cause catastrophic engine damage and potential loss of aircraft control. This rule prevents accidents caused by worn or improperly installed circlips by mandating replacement and proper technique."}},"importantCases":[],"_links":{"self":"/api/acts/ad-om-p-4-piston-pin-circlip-replacement-and-installation-procedure","history":"/api/acts/ad-om-p-4-piston-pin-circlip-replacement-and-installation-procedure/history","analysis":"/api/acts/ad-om-p-4-piston-pin-circlip-replacement-and-installation-procedure/analysis","conflicts":"/api/acts/ad-om-p-4-piston-pin-circlip-replacement-and-installation-procedure/conflicts","importantCases":"/api/acts/ad-om-p-4-piston-pin-circlip-replacement-and-installation-procedure/important-cases","documents":"/api/acts/ad-om-p-4-piston-pin-circlip-replacement-and-installation-procedure/documents"}}