{"id":"F2006B02478","name":"AD/AS 355/23 - Hydraulic System","slug":"ad-as-355-23-hydraulic-system","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41734,"registerId":"commonwealth-F2006B02478-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AS 355/23 - Hydraulic System","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 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  Eurocopter AS 355 (Twin Ecureuil) Series Helicopters\n\n \n\nAD/AS 355/23 Hydraulic System 12/86 DM\n\n \n\nApplicability: All model AS 355 E, F, F1 and F2 helicopters.\n\n \n\nRequirement: Action in accordance with Aerospatiale AS 355 Service Bulletin No. 29-01.\n\n \n\nNote: French AD 86-150-30(B) refers.\n\n \n\nCompliance: Within 300 hours time in service after 30 November 1986 or before 31 January 1987 whichever occurs first.\n\n \n\nFor spares: before installation in an aircraft after 30 November 1986.\n\n \n\nBackground:  A spring spacer is fitted to prevent an overpressure in the hydraulic systems if the flange of the regulator valve stem, fitted to the filter unit, should come off.\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 directive applies to all AS 355 E, F, F1 and F2 helicopters, prescribes compliance with a specific Aerospatiale Service Bulletin, sets a fixed compliance window and places a pre-installation requirement on spares. The text contains no indication that the scope (the set of affected models, the required action, or the compliance deadlines) has been altered from the instrument as published."},"complexity_factors":["Technical mechanical intervention required (fitting a spring spacer to a hydraulic regulator/filter) increases specialist maintenance complexity.","Cross-reference to an external technical document (Aerospatiale AS 355 Service Bulletin No. 29-01) — implementers must obtain and follow that bulletin precisely.","Time-limited compliance window (300 hours after 30 Nov 1986 or before 31 Jan 1987) requires scheduling and may interact with operational hours accounting.","Applicability limited to specific aircraft models (AS 355 E, F, F1, F2) — requires accurate fleet identification by operators.","Requirement for spares to be compliant before installation introduces procurement and supply‑chain constraints for parts suppliers and maintenance providers.","Safety-critical nature of hydraulic systems raises operational risk if the mandated action or the Service Bulletin is not performed correctly."],"plain_english_summary":"The directive mandates fitting a spring spacer in the hydraulic regulator/filter assembly of all Eurocopter AS 355 E/F/F1/F2 helicopters to prevent hydraulic overpressure if the regulator valve‑stem flange separates. Operators and spare-part suppliers must comply per Aerospatiale AS 355 Service Bulletin No. 29-01 within 300 flight hours after 30 Nov 1986 or by 31 Jan 1987, with parts and installation costs borne by operators and maintenance providers."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, single-issue airworthiness directive addressing a specific mechanical defect in a specific aircraft type. It has not expanded beyond its original purpose of mandating a safety modification to prevent hydraulic overpressure."},"complexity_factors":["Very short document (approximately 150 words of substantive content)","Only 4 defined applicability criteria (specific helicopter models)","Single technical requirement referencing an external document (Service Bulletin No. 29-01)","Simple compliance deadline structure (hours-based OR calendar-based, whichever first)","No nested exceptions, conditional logic, or cross-references to other legislation","Minimal defined terms — only standard aviation terminology (time in service, spares)","Straightforward background explanation of the safety issue"],"plain_english_summary":"**What this is:** An Airworthiness Directive (AD) — essentially a mandatory safety notice issued by Australia's Civil Aviation Safety Authority (CASA) for specific helicopters.\n\n**Who it affects:** Owners and operators of Eurocopter AS 355 E, F, F1 and F2 model helicopters (also known as the \"Twin Ecureuil\"). These are twin-engine light utility helicopters commonly used for corporate transport, emergency services, and aerial work.\n\n**What it requires:** Operators must follow the instructions in Aerospatiale Service Bulletin No. 29-01. This involves fitting a **spring spacer** — a small mechanical component — to the hydraulic system. The spacer acts as a safety backup: if the flange (a rim or collar) on the regulator valve stem breaks or comes loose, the spacer prevents dangerous overpressure in the hydraulic system that could cause system failure.\n\n**When it had to be done:** The work had to be completed within 300 flight hours after 30 November 1986, or before 31 January 1987 — whichever came first. For spare parts, any hydraulic components had to be modified before being installed in an aircraft after that same November 1986 date.\n\n**Why it matters:** Hydraulic system failures in helicopters can lead to loss of flight control. This AD addresses a specific design flaw where a part could detach and cause dangerous pressure buildup. The reference to French AD 86-150-30(B) indicates this was a coordinated international safety response — the same issue was flagged by French aviation authorities (Aerospatiale being a French manufacturer)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-as-355-23-hydraulic-system","history":"/api/acts/ad-as-355-23-hydraulic-system/history","analysis":"/api/acts/ad-as-355-23-hydraulic-system/analysis","conflicts":"/api/acts/ad-as-355-23-hydraulic-system/conflicts","importantCases":"/api/acts/ad-as-355-23-hydraulic-system/important-cases","documents":"/api/acts/ad-as-355-23-hydraulic-system/documents"}}