{"id":"F2006B06374","name":"AD/PT6T/4 - Fuel Control Bypass Valve Diaphragm","slug":"ad-pt6t-4-fuel-control-bypass-valve-diaphragm","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":47639,"registerId":"commonwealth-F2006B06374-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/PT6T/4 - Fuel Control Bypass Valve Diaphragm","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)  Pratt and Whitney Canada Turbine Engines - PT6T Series\n\n \n\nAD/PT6T/4 Fuel Control Bypass Valve Diaphragm 10/85\n\nApplicability: PT6T-3 and PT6T-6 engines fitted with Aviation Electric Fuel Control Units P/N 2524381-5, 3244712-1 and -2, 3244717-1 thru -5, 3244721-1 thru -5, 3244735-1 thru\n\n-7, and 3244737-1 thru -7.\n\n \n\nDocument: 1. Pratt & Whitney Aircraft of Canada Alert SB No. 5153; or 2. FAA AD 78-17-05, Amendment 39-3285; or\n\n3. AD/UAC-T/30.\n\n \n\nCompliance: Within the next 50 hours time in service after 30 November 1978.\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\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, single-issue airworthiness directive focused on a specific mechanical defect in specific engine models. It has not expanded beyond its original safety purpose."},"complexity_factors":["Very short document (under 200 words)","Only 4 defined applicability criteria (engine models + specific part numbers)","Single compliance requirement with clear deadline","No nested exceptions or conditional logic","No cross-references to other legislation sections","Straightforward technical reference to manufacturer service bulletin"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) that requires specific maintenance action on aircraft engines.\n\n**What it does:**\nOrders owners and operators of certain Pratt & Whitney Canada PT6T-3 and PT6T-6 turbine engines to inspect or replace the **fuel control bypass valve diaphragm** — a rubber or synthetic membrane that helps regulate fuel flow. If this diaphragm fails, it can cause engine problems including potential power loss or fuel leaks.\n\n**Who it affects:**\nAnyone operating aircraft with these specific engine models **AND** specific fuel control units (identified by part numbers like 2524381-5, 3244712-1, etc.). This typically includes helicopter operators and some fixed-wing aircraft using these popular \"Twin Pac\" engines.\n\n**What must be done:**\nThe work must be completed within **50 flight hours** after 30 November 1978 (the original compliance date from when this AD was first issued).\n\n**Why it matters:**\nAirworthiness Directives are legally enforceable. Ignoring them means an aircraft cannot legally fly in Australian airspace. This particular AD addresses a known defect that could compromise engine reliability and flight safety.\n\n**Key documents referenced:**\nThe technical instructions come from Pratt & Whitney's Alert Service Bulletin 5153, or equivalent FAA (US) directives."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The text supplied sets out the AD's scope (engine models and specified fuel-control-unit part numbers), the acceptable reference documents, and the compliance deadline. The document as provided contains no language indicating an expansion or narrowing of scope from an earlier version; there is no evidence in the supplied text that the scope has changed from an original intent."},"complexity_factors":["Narrow technical applicability confined to two engine models but many specific fuel-control-unit part numbers (requires careful parts matching). (Applicability)","Mandatory reliance on external technical documents rather than inclusion of procedures in the AD increases procedural complexity and information-gathering burden. (Document)","Short compliance window (50 hours time in service after a specific date) increases scheduling and operational pressure for affected operators. (Compliance)","Work is technical maintenance (fuel control bypass valve diaphragm) requiring qualified personnel and possible parts, which can create logistical complexity not described in the AD text. (Applicability; Document)","Multiple acceptable documents provide alternatives but require the operator to choose and verify equivalence, adding a decision point. (Document)"],"plain_english_summary":"This AD mandates owners/operators of Pratt & Whitney PT6T-3 and PT6T-6 engines fitted with the listed Aviation Electric Fuel Control unit part numbers to inspect/repair the fuel-control bypass valve diaphragm by following one of three referenced documents (P&W ASB No.5153, FAA AD 78-17-05, or AD/UAC‑T/30). Work must be done within 50 hours TIS after 30 Nov 1978. Compliance (and its cost) is the operator’s responsibility; the referenced documents set the specific maintenance steps."}},"importantCases":[],"_links":{"self":"/api/acts/ad-pt6t-4-fuel-control-bypass-valve-diaphragm","history":"/api/acts/ad-pt6t-4-fuel-control-bypass-valve-diaphragm/history","analysis":"/api/acts/ad-pt6t-4-fuel-control-bypass-valve-diaphragm/analysis","conflicts":"/api/acts/ad-pt6t-4-fuel-control-bypass-valve-diaphragm/conflicts","importantCases":"/api/acts/ad-pt6t-4-fuel-control-bypass-valve-diaphragm/important-cases","documents":"/api/acts/ad-pt6t-4-fuel-control-bypass-valve-diaphragm/documents"}}