{"id":"F2006B08323","name":"AD/CESSNA 400/37 - Crankcase Oil Separator Return Line Check Valve - Incorporation of","slug":"ad-cessna-400-37-crankcase-oil-separator-return-line-check-valve-incorporation-of","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115730,"registerId":"commonwealth-F2006B08323-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CESSNA 400/37 - Crankcase Oil Separator Return Line Check Valve - Incorporation of","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)  Cessna 400 Series Aeroplanes\n\n \n\nAD/CESSNA 400/37 Crankcase Oil Separator Return Line\n\nCheck Valve - Incorporation of\n\n\n8/73\n\n \n\nApplicability: Model 421B S/Nos. 421B0260 to 421B0346 fitted with new Airesearch TH0871 turbochargers with S/No. prefixes BC or later. S/Nos. 421B0001 to 421B0259 fitted with new Airesearch TH0871 turbochargers with S/No. prefixes BC or later or with remanufactured Airesearch TH0871 turbo-chargers with S/No. prefixes BCR or later.\n\n \n\nDocument: 1. Cessna SL ME73-10; or\n\n \n\n2. FAA AD 73-13-8.\n\n \n\nEffective: 28 September 1973.\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\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 from 1973 addressing a specific mechanical defect. It has not expanded beyond its original purpose of mandating a check valve installation for oil separator return lines on specific Cessna aircraft."},"complexity_factors":["Single, specific mechanical modification (one check valve installation)","Narrow applicability limited to one aircraft model (Cessna 421B) with specific serial number ranges and turbocharger configurations","Only two compliance documents referenced (Cessna service letter and FAA AD)","No defined terms section or complex conditional logic","Effective date is absolute (28 September 1973) with no phased compliance or exceptions","Total length is extremely short (under 200 words of substantive content)"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). It requires specific Cessna 400 series aircraft to install a check valve on the crankcase oil separator return line.\n\n**What it does:**\n- Mandates a mechanical modification to prevent engine oil from flowing backwards through the return line\n- Applies only to Cessna Model 421B aircraft with specific serial numbers and particular Airesearch turbocharger models\n\n**Who it affects:**\n- Owners and operators of Cessna 421B aircraft (serial numbers 421B0260 to 421B0346 with new turbochargers, or 421B0001 to 421B0259 with new or remanufactured turbochargers)\n- Maintenance organisations servicing these aircraft\n\n**Why it matters:**\nWithout this check valve, oil could flow the wrong way, potentially causing engine damage or failure. This is a **safety-critical** fix — non-compliance means the aircraft cannot legally fly.\n\n**Compliance documents:**\nOperators must follow either Cessna Service Letter ME73-10 or the equivalent US Federal Aviation Administration directive (FAA AD 73-13-8)."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The document, as presented, states a focused requirement: incorporation of a crankcase oil separator return line check valve on the listed Cessna 421B aeroplanes and refers to specific procedural documents. There is no internal indication within this text that the scope has been broadened or narrowed from the instrument’s stated objective; the Applicability and Document sections define the vehicle population and the procedural references, and the Effective date fixes when the requirement applied."},"complexity_factors":["Narrow technical scope limited to a specific aircraft model (Cessna 421B) and specified serial-number ranges (Applicability section).","Dependence on external technical documents (Cessna SL ME73-10 or FAA AD 73-13-8) for the actual installation procedure (Document section).","Identification of affected units by combinations of airframe serial numbers and turbocharger serial-number prefixes, requiring cross-referencing maintenance records.","No cost, time, or alternative-compliance details in the directive itself—operators must consult referenced documents or the regulator for implementation specifics.","Regulatory enforcement and record-keeping obligations implicit in airworthiness directives, though not detailed in this short text."],"plain_english_summary":"This AD requires fitting a check valve in the crankcase oil‑separator return line on specified Cessna 421B aeroplanes identified by airframe and turbocharger serial‑number ranges. It affects owners, operators and maintenance organizations who must arrange and pay for the modification to keep the aircraft airworthy. The AD delegates the detailed installation procedure to Cessna Service Letter ME73‑10 or FAA AD 73‑13‑8 and took effect 28 September 1973."}},"importantCases":[],"_links":{"self":"/api/acts/ad-cessna-400-37-crankcase-oil-separator-return-line-check-valve-incorporation-of","history":"/api/acts/ad-cessna-400-37-crankcase-oil-separator-return-line-check-valve-incorporation-of/history","analysis":"/api/acts/ad-cessna-400-37-crankcase-oil-separator-return-line-check-valve-incorporation-of/analysis","conflicts":"/api/acts/ad-cessna-400-37-crankcase-oil-separator-return-line-check-valve-incorporation-of/conflicts","importantCases":"/api/acts/ad-cessna-400-37-crankcase-oil-separator-return-line-check-valve-incorporation-of/important-cases","documents":"/api/acts/ad-cessna-400-37-crankcase-oil-separator-return-line-check-valve-incorporation-of/documents"}}