{"id":"F2006B02118","name":"AD/AC/6 - Fuel Vent and Vapour Return Lines - Modification","slug":"ad-ac-6-fuel-vent-and-vapour-return-lines-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41348,"registerId":"commonwealth-F2006B02118-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AC/6 - Fuel Vent and Vapour Return Lines - Modification","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-description: CASA Airworthiness Directive\nmeta-generator: Aspose.Words for .NET 22.10.0\nmeta-keywords: Issue NK,Aircraft below 5700 kg,Twin Commander (Gulfstream/Rockwell/ Aerocommander 500, 600 and 700) Series Aeroplanes,Fuel Vent and Vapour Return Lines - Modification,6\ntitle: Airworthiness Directive - AD/AC/6 - Fuel Vent and Vapour Return Lines - Modification\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)  Twin Commander (Gulfstream/Rockwell/ Aerocommander 500, 600 and 700) Series Aeroplanes\n\n \n\nAD/AC/6 Fuel Vent and Vapour Return Lines - Modification NK\n\nApplicability: Models 560A and 680: S/Nos. 231 to 580 except 466, 471, 492, 509, 523, 547, 568,\n\n570, 572, 574, 576, 579.\n\n \n\nDocument: 1. Aero Commander SB No. 45; or\n\n \n\n2. FAA AD 58-1-1.\n\n \n\nCompliance: Forthwith.\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":"Based on the text provided, the directive's scope is explicit and limited to specified Twin Commander Model 560A and 680 aeroplanes within a defined serial-number range with listed exceptions. The AD delegates technical instruction to two referenced documents and mandates immediate compliance. There is no indication in the supplied extract that the scope has been broadened or narrowed from an earlier or original intent."},"complexity_factors":["Narrow and specific applicability by model and a detailed serial-number range with multiple explicit exceptions (Applicability).","Immediate ('Forthwith') compliance requirement reducing scheduling flexibility (Compliance).","Technical content and procedural detail are outsourced to external documents (Aero Commander SB No. 45 or FAA AD 58-1-1), so the AD itself is short but dependent on other texts (Document).","Enforcement and cost allocation are straightforward (owners/operators pay), but verifying applicability (serial numbers) and coordinating maintenance create practical complexity.","Lacks in-text procedural steps, creating reliance on maintenance organisations to interpret and apply the referenced documents correctly."],"plain_english_summary":"This Airworthiness Directive (AD/AC/6) requires a physical modification to the fuel vent and vapour return lines on certain Twin Commander aeroplanes. Mechanically, it directs that the modification be carried out in accordance with one of two external technical documents: Aero Commander Service Bulletin No. 45 or FAA AD 58-1-1 (Document). The directive applies only to Model 560A and Model 680 aeroplanes with serial numbers 231 through 580, excluding the specific serial numbers 466, 471, 492, 509, 523, 547, 568, 570, 572, 574, 576 and 579 (Applicability). It requires compliance immediately (Compliance: Forthwith).\n\nWho this affects\n- Owners and operators of Twin Commander Model 560A and 680 aeroplanes whose serial numbers fall inside the specified range but are not one of the excluded serial numbers (Applicability). \n- Maintenance organisations and engineers who will perform the modification by following the referenced technical documents (Document).\n\nWhat the directive does, in practice\n- Identifies the set of aircraft to be modified (Applicability). \n- Directs that the modification be performed according to Aero Commander SB No. 45 or FAA AD 58-1-1 (Document). \n- Sets an immediate compliance requirement: the work must be done forthwith (Compliance).\n\nWho pays and who decides\n- The owners/operators of the affected aircraft are the parties who must arrange and pay for the modification: parts, labour and any associated aircraft downtime. This follows from the directive applying to specific aircraft and requiring action forthwith (Applicability; Compliance). \n- The Civil Aviation Safety Authority issues the directive and enforces compliance; the technical means of compliance are delegated to the two referenced documents (Document).\n\nImplementation mechanics and immediate trade-offs\n- The AD delegates technical detail to external service documents (Document). That means the AD itself does not contain step-by-step instructions; operators must consult the referenced SB or FAA AD to know exactly what to do. \n- Costs incurred are tangible (parts, labour, maintenance scheduling, aircraft out-of-service time). The AD’s immediate compliance requirement (Compliance: Forthwith) reduces scheduling flexibility and may increase short-term disruption. \n- Responsibility for correctly identifying whether an aircraft is in the affected group rests with the owner/operator (Applicability). That requires checking serial numbers against the list and exceptions.\n\nCompliance burden and discretion\n- The directive imposes a clear, time-sensitive compliance obligation on owners/operators (Compliance). \n- Technical discretion about how to perform the modification is limited by the requirement to follow one of the two specified documents; within those documents, maintenance providers may have routine professional discretion about methods, parts sourcing and record-keeping (Document). \n\nRisks and practical considerations\n- Practical implementation risks include misidentifying an aircraft’s serial number, availability of parts or qualified maintenance resources, and scheduling downtime to carry out the modification (Applicability; Compliance). \n- The AD does not itself state the operational reason for the modification or quantify costs; it simply mandates the modification and points to the documents that contain the technical instructions (Document)."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This AD maintains its original narrow scope. It targets a specific airworthiness issue (fuel vent/vapour return lines) in a specific aircraft type (Twin Commander 560A/680) with specific serial numbers. There is no evidence of scope creep; it remains a targeted safety directive for a known mechanical defect."},"complexity_factors":["Extremely short document (under 200 words)","Only 2 defined applicability criteria (model numbers and serial number ranges)","Simple exclusion list (12 specific serial numbers excluded from a range)","No cross-references to other legislation beyond the enabling Civil Aviation Regulations 1998","No conditional logic or nested exceptions — compliance is absolute and immediate","References only 2 external technical documents for implementation details"],"plain_english_summary":"**What this is:** This is an Airworthiness Directive (AD) — a mandatory safety order issued by the Civil Aviation Safety Authority (CASA). Think of it like a compulsory recall notice for aircraft, but issued by the aviation regulator instead of a manufacturer.\n\n**What it requires:** Owners and operators of specific Twin Commander aircraft (models 560A and 680 with serial numbers 231–580, excluding a long list of exceptions) must modify their **fuel vent and vapour return lines** immediately (\"forthwith\").\n\n**Why it matters:** Fuel vent and vapour return lines prevent fuel tanks from pressurising or vacuum-locking, and stop dangerous fuel vapours from building up. A fault here could cause fuel leaks, engine failure, or fire. This AD addresses a known safety defect in these specific aircraft.\n\n**Who must comply:** Anyone operating the affected Twin Commander models in Australia. The directive references two technical documents that explain exactly how to do the modification:\n- Aero Commander Service Bulletin No. 45, or\n- FAA Airworthiness Directive 58-1-1 (the original US safety order)\n\n**The bottom line:** If you own one of these specific aircraft, you cannot legally fly it until this fuel system modification is done. No exceptions, no delays — \"forthwith\" means immediately."}},"importantCases":[],"_links":{"self":"/api/acts/ad-ac-6-fuel-vent-and-vapour-return-lines-modification","history":"/api/acts/ad-ac-6-fuel-vent-and-vapour-return-lines-modification/history","analysis":"/api/acts/ad-ac-6-fuel-vent-and-vapour-return-lines-modification/analysis","conflicts":"/api/acts/ad-ac-6-fuel-vent-and-vapour-return-lines-modification/conflicts","importantCases":"/api/acts/ad-ac-6-fuel-vent-and-vapour-return-lines-modification/important-cases","documents":"/api/acts/ad-ac-6-fuel-vent-and-vapour-return-lines-modification/documents"}}