{"id":"F2006B07321","name":"AD/TB20/18 - Fuel System","slug":"ad-tb20-18-fuel-system","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":49349,"registerId":"commonwealth-F2006B07321-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/TB20/18 - Fuel System","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nAerospatiale (Socata) TB20 (Trinidad) Series Aeroplanes\n\nAD/TB20/18 Fuel System 10/90\n\nApplicability: Model TB20 and TB21 with serial numbers 1 through 730.\n\nRequirement: For model TB20: Install a check valve into the fuel system in accordance with Socata Service Bulletin number 47/1 and kit 9128.\n\nFor model TB20 and TB21: Replace the Dukes pump P/N 463400 with a Weldon pump P/N TB20/6101/5000 (TB20) or P/N TB20/6101/5003 (TB21) respectively in accordance with kits 9132 and 9133.\n\nNote: DGAC AD 89-183-(A)R1 refers.\n\nCompliance: Prior to 31 October 1991.\n\nBackground: The inability of the normally fitted electric fuel boost pump to operate in a dry condition if the engine driven fuel pump loses its prime when the engine is stopped, could result in air being drawn into the fuel lines causing power interruption or loss. Installation of a check valve will prevent fuel from siphoning back into the fuel tank when the engine is stopped and the fuel selector is not in the off position; and installation of an electric fuel boost pump which incorporates a solid rotor design, will displace air in the system within its operating parameters.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete airworthiness directive with a narrow, specific scope (particular aircraft models, specific serial numbers, specific mechanical fixes). It has not expanded beyond its original purpose of addressing a specific fuel pump priming failure risk."},"complexity_factors":["Very short document (under 300 words)","Only 2 defined models and specific serial number range","Two distinct but simple mechanical modifications required","Single compliance deadline with no conditional extensions","No nested exceptions or complex cross-referencing (only one reference to a French aviation authority document for context)","Clear, single-purpose safety directive with straightforward technical requirements"],"plain_english_summary":"This CASA safety directive mandated installation of a one‑way check valve on Socata TB20 fuel systems and replacement of Dukes electric boost pumps with Weldon solid‑rotor pumps on affected TB20/TB21 aircraft to stop fuel siphoning and make pumps tolerant of air. It applied to TB20/TB21 serial numbers 1–730 and required compliance by 31 October 1991 to prevent in‑flight engine cut‑outs from air in the fuel lines."},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"The directive's scope aligns with its stated safety objective in the text: it targets TB20/TB21 aeroplanes (s/n 1–730) and mandates a check valve installation plus pump replacement per the manufacturer kits. The instrument prescribes these specific mechanical interventions and a compliance date; the text does not indicate any expansion or narrowing beyond that original technical intent."},"complexity_factors":["Technical installation required (check valve and different model pump) using specified service bulletins and kit numbers","Narrow applicability by model and serial numbers (TB20/TB21, s/n 1–730) requiring verification of airframe identity","Different replacement part numbers for TB20 vs TB21 (model-specific kits)","Compliance deadline imposes scheduling and maintenance planning burdens","Need to source specific parts/kits (supply-chain and cost implications for owners/operators)","Mandated change affects certified equipment and airworthiness status, requiring maintenance records and potential inspection","Reference to foreign AD (DGAC AD 89-183-(A)R1) may require cross-jurisdictional coordination"],"plain_english_summary":"This Civil Aviation Safety Authority Airworthiness Directive requires owners/operators of Aerospatiale (Socata) TB20 and TB21 aeroplanes (serials 1–730) to install a check valve and replace the factory Dukes electric boost pump with a specified Weldon pump, using the manufacturer service bulletins and kit numbers provided. The mechanical changes are intended to stop fuel siphoning and ensure the boost pump can displace air if the engine-driven pump loses prime. Compliance was required by 31 October 1991; owners/operators bear the costs and must install the kits to maintain airworthiness."}},"importantCases":[],"_links":{"self":"/api/acts/ad-tb20-18-fuel-system","history":"/api/acts/ad-tb20-18-fuel-system/history","analysis":"/api/acts/ad-tb20-18-fuel-system/analysis","conflicts":"/api/acts/ad-tb20-18-fuel-system/conflicts","importantCases":"/api/acts/ad-tb20-18-fuel-system/important-cases","documents":"/api/acts/ad-tb20-18-fuel-system/documents"}}