{"id":"F2006B02110","name":"AD/AC/50 - Unfeathering Pump Supply Line - Replacement","slug":"ad-ac-50-unfeathering-pump-supply-line-replacement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41340,"registerId":"commonwealth-F2006B02110-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AC/50 - Unfeathering Pump Supply Line - Replacement","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 8/1973,Aircraft below 5700 kg,Twin Commander (Gulfstream/Rockwell/ Aerocommander 500, 600 and 700) Series Aeroplanes,Unfeathering Pump Supply Line - Replacement,50\ntitle: Airworthiness Directive - AD/AC/50 - Unfeathering Pump Supply Line - Replacement\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/50 Unfeathering Pump Supply Line - Replacement 8/73\n\nApplicability: Model 690 with S/Nos. 11001 to 11063. Document:  1. Aero Commander SB No. 123A; or 2.              FAA AD 73-13-9.\n\nCompliance: Within 100 hours’ time in service after 31 August 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","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"Based on the text provided, the scope has not changed from the instrument's stated intent. The directive is limited to Model 690 aircraft with serial numbers 11001–11063, requires replacement of the unfeathering pump supply line, and specifies compliance within 100 hours after 31 August 1973, with the procedural details to be followed from the referenced documents (Applicability; Document; Compliance). The text contains no indication of an expanded scope or amendment beyond those elements."},"complexity_factors":["Very narrow applicability (specific model and serial number range) (Applicability)","Single, clearly stated mandatory action (replacement of a component) (plain text of AD title and Compliance)","Short, fixed compliance window (100 hours after 31 August 1973) (Compliance)","Reliance on external technical documents (Aero Commander SB No. 123A or FAA AD 73-13-9) for procedural details (Document)","No alternative compliance method or exemption described in the instrument (implicit in the text)"],"plain_english_summary":"Summary of required change\n\n- What the instrument does mechanically: It mandates replacement of the unfeathering pump supply line on certain Twin Commander Model 690 aeroplanes. The action must be carried out in accordance with either Aero Commander Service Bulletin No. 123A or FAA Airworthiness Directive 73-13-9 (Document). The directive applies only to Model 690 aircraft with serial numbers 11001 to 11063 (Applicability). The replacement must be completed within 100 hours' time in service after 31 August 1973 (Compliance).\n\nStated purpose and how that maps to effects\n\n- The directive’s stated purpose is implicit in the title and the nature of airworthiness directives: it requires a part replacement to address a condition judged by the issuing authority to be relevant to the aircraft’s airworthiness. The source text does not set out a detailed failure mode or consequence; it specifies the required corrective action and the normative documents to follow (Document).\n\nWho pays, who decides, and what changes in behaviour\n\n- Who pays: The owner/operator of any affected Model 690 is responsible for the cost of the replacement (Applicability; Compliance). Costs include the parts, labour, and any associated downtime.\n- Who decides: The Civil Aviation Safety Authority issued the directive; compliance is achieved by following the named service bulletin or FAA AD referenced in the instrument (Document). Maintenance providers perform the physical replacement under the direction of the operator and in accordance with approved procedures.\n- What behaviour changes: Operators of affected serial-numbered aircraft must schedule and carry out the replacement within the specified 100‑hour compliance window; they may reschedule flights or combine the work with other maintenance to minimise disruption (Compliance).\n\nCompliance, incentives and administrative discretion\n\n- Compliance requirement: The replacement is mandatory within the stated time limit; the directive points to external documents that contain the technical steps or part numbers to be used (Document; Compliance).\n- Incentives: Operators have a direct regulatory incentive to comply in order to maintain airworthiness certification. Non‑compliance risks regulatory action and potential grounding of the aircraft.\n- Administrative discretion: The AD itself prescribes the action and the reference documents, so the operator’s discretion is limited to scheduling and selecting an appropriately authorised maintenance provider. Any technical interpretation or method must align with the referenced service bulletin or FAA AD (Document).\n\nCosts, trade-offs and implementation risks (mechanical view)\n\n- Direct costs: parts and labour for replacement and aircraft downtime are borne by the operator (Applicability; Compliance).\n- Trade-offs & opportunity cost: Operators must divert maintenance resources and aircraft availability toward this mandatory work within the stated window; that may shift the timing of commercial operations or other maintenance tasks.\n- Implementation risks: If the referenced service bulletin or FAA AD lacks sufficient detail, or if parts are scarce (not addressed in the source text), operators may face delays or need additional approvals from the regulator to substitute procedures. The instrument itself does not specify alternative compliance methods or exemptions (Document).\n\nNet mechanical effect\n\n- The directive creates a narrowly targeted mandatory maintenance task applying only to Model 690 serial numbers 11001–11063, to be done according to specified technical documents within a short, stated compliance window. This imposes a one‑time resource and scheduling burden on the affected aircraft’ owners/operators while removing the identified component from service as required by the referenced documents (Applicability; Document; Compliance)."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific mechanical defect in a specific aircraft model. It has not expanded beyond its original purpose of mandating replacement of a faulty unfeathering pump supply line."},"complexity_factors":["Extremely short document — approximately 150 words of substantive content","Only one defined term implicitly referenced (\"time in service\")","No cross-references to other legislation beyond the enabling regulations (Civil Aviation Regulations 1998, Part 39)","Single, unambiguous compliance action (replacement of one component)","Clear applicability criteria (specific model and serial number range)","No conditional logic, exceptions, or nested provisions","Binary compliance pathway (follow either of two referenced documents)"],"plain_english_summary":"**What this is:** This is an Airworthiness Directive (AD) — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). Think of it like a compulsory recall notice, but for aircraft parts.\n\n**What it requires:** Owners and operators of specific Twin Commander aeroplanes (models 500, 600, and 700 series, specifically Model 690 with serial numbers 11001 to 11063) must replace the \"unfeathering pump supply line.\" The unfeathering pump is a critical component that helps restart a propeller engine if it fails in flight (when a propeller \"feathers\" — turns edge-on to reduce drag — you need this pump to \"unfeather\" it and get the engine going again).\n\n**Why it matters:** A faulty supply line could mean the pump doesn't work when needed. If an engine fails and you can't unfeather the propeller, you lose the ability to restart that engine, which is a serious safety risk — especially in a twin-engine aircraft where you rely on the second engine to keep flying.\n\n**Who must comply:** Anyone operating the affected aircraft models. They have a deadline: the replacement must be done within 100 hours of flight time after 31 August 1973.\n\n**How to comply:** Follow either the manufacturer's Service Bulletin (Aero Commander SB No. 123A) or the equivalent American FAA directive (FAA AD 73-13-9)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-ac-50-unfeathering-pump-supply-line-replacement","history":"/api/acts/ad-ac-50-unfeathering-pump-supply-line-replacement/history","analysis":"/api/acts/ad-ac-50-unfeathering-pump-supply-line-replacement/analysis","conflicts":"/api/acts/ad-ac-50-unfeathering-pump-supply-line-replacement/conflicts","importantCases":"/api/acts/ad-ac-50-unfeathering-pump-supply-line-replacement/important-cases","documents":"/api/acts/ad-ac-50-unfeathering-pump-supply-line-replacement/documents"}}