{"id":"F2006B07325","name":"AD/TB20/21 - Propeller Deicing Electrical Circuit Protection","slug":"ad-tb20-21-propeller-deicing-electrical-circuit-protection","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":49360,"registerId":"commonwealth-F2006B07325-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/TB20/21 - Propeller Deicing Electrical Circuit Protection","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)  Aerospatiale (Socata) TB20 (Trinidad) Series Aeroplanes\n\n \n\nAD/TB20/21 Propeller Deicing Electrical Circuit Protection 10/91\n\nApplicability: All TB20 and TB21 aircraft as specified in the requirement document. Requirement:  Action in accordance with Aerospatiale TB Airplanes - SB Nr. 59.\n\nCompliance: Prior to 3 October 1992.\n\n \n\nBackground: Compliance with this AD is necessary in order to ensure the integrity of the propeller de icing circuit by installing the correct rating fuse.\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\n \n\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-limited safety directive with a single purpose. It has not expanded beyond its original intent of ensuring proper fuse installation in the propeller de-icing circuit."},"complexity_factors":["Extremely short document (under 200 words)","Only 2 defined applicability criteria (TB20 and TB21 aircraft)","Single, unambiguous compliance action (install correct fuse per manufacturer bulletin)","No nested exceptions or conditional logic","No cross-references to other legislation beyond the parent Civil Aviation Regulations 1998","Clear deadline (3 October 1992)"],"plain_english_summary":"**What this is:** This is an Airworthiness Directive (AD) — essentially a mandatory safety notice issued by Australia's Civil Aviation Safety Authority (CASA) for specific aircraft.\n\n**What it does:** It requires owners or operators of certain Socata TB20 and TB21 aeroplanes (known as \"Trinidad\" models) to install a fuse with the correct electrical rating in the propeller de-icing system. A fuse is a safety device that breaks an electrical circuit if too much current flows through it, preventing fires or equipment damage.\n\n**Who it affects:** Anyone who owns, operates, or maintains Aerospatiale (Socata) TB20 or TB21 series aircraft.\n\n**Why it matters:** The propeller de-icing system prevents ice buildup on propeller blades during flight. If the wrong fuse is installed, the electrical circuit protecting this system could fail — potentially causing the de-icing system to malfunction or creating a fire risk. This directive ensures the safety system works as designed.\n\n**What had to happen:** Aircraft operators had to complete this modification before 3 October 1992, following the manufacturer's Service Bulletin (SB) number 59."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The instrument's scope, as presented in the text supplied, applies specifically to TB20 and TB21 aircraft and requires compliance with Aerospatiale SB Nr. 59 prior to 3 October 1992. There is no text in the supplied document indicating a change to that scope from an earlier version; the directive sets a single technical obligation and a compliance date."},"complexity_factors":["Single, narrowly targeted technical requirement (install correct rating fuse) rather than multiple provisions","Limited applicability to a defined set of aircraft models (TB20 and TB21) as stated in Applicability","Technical detail is delegated to an external document (Aerospatiale TB Airplanes - SB Nr. 59), so legal text is short but depends on an external technical source","Fixed, near-term compliance deadline (prior to 3 October 1992) creates a binary compliance outcome","Regulatory context is clear (airworthiness directive under Civil Aviation Regulations Part 39), so enforcement pathway is straightforward"],"plain_english_summary":"What this directive does (mechanically):\n\n- Requires the installation of the correctly rated fuse in the propeller deicing electrical circuit on the specified Aerospatiale (Socata) TB20 and TB21 aeroplanes. (Requirement; Applicability)\n- Directs that the work be carried out in accordance with \"Aerospatiale TB Airplanes - SB Nr. 59\" (the referenced service bulletin). (Requirement)\n- Sets a compliance timeframe: the change must be completed prior to 3 October 1992. (Compliance)\n- Is issued under the Commonwealth civil aviation framework for airworthiness directives (Civil Aviation Regulations, Part 39, Schedule of Airworthiness Directives). (header)\n\nOfficial stated purpose:\n\n- The document states the change is intended to “ensure the integrity of the propeller de icing circuit by installing the correct rating fuse.” (Background)\n\nWho is affected and who decides or pays:\n\n- Affected parties: owners and operators of the TB20 and TB21 aircraft identified in the applicability statement. (Applicability)\n- Who decides/authorises: the directive is issued under the Civil Aviation Regulations framework and is part of the Schedule of Airworthiness Directives; the Civil Aviation Safety Authority is the regulatory context shown on the instrument. (header)\n- Who pays: owners/operators must arrange and pay for compliance (parts and labour) to implement the service bulletin requirement. (Applicability; Requirement)\n\nPractical compliance implications, incentives and trade-offs:\n\n- Compliance action: obtain and fit the fuse specified or otherwise follow the procedures in SB Nr. 59. The directive points to that external technical document for the exact technical steps. (Requirement)\n- Direct cost and time: aircraft operators will incur the cost of the fuse, any other parts, and maintenance labour needed to carry out the work before the deadline. (Requirement; Compliance)\n- Incentives: completing the mandated installation avoids regulatory non-compliance and aligns the aircraft with the stated airworthiness objective; it also removes whatever operational risk the regulator intended to address by correcting the fuse rating. (Background; Requirement)\n- Implementation risk and administrative discretion: the quality of implementation depends on the clarity and technical content of the referenced service bulletin (SB Nr. 59). The directive itself delegates technical detail to that SB, so maintenance organisations must follow the SB to meet the AD. (Requirement)\n- Enforcement risk: the AD is part of the airworthiness directives schedule and therefore subject to regulatory oversight under the cited civil aviation regulations; the AD sets a clear compliance date which creates a compliance window. (header; Compliance)\n\nWhere to find the technical steps:\n\n- The detailed technical procedure and exact fuse specification are contained in Aerospatiale TB Airplanes - SB Nr. 59, which the directive makes mandatory for the affected aircraft. (Requirement)\n\nSource citations: header (Civil Aviation Regulations Part 39), Applicability, Requirement (SB Nr. 59), Compliance (due date), Background (stated rationale)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-tb20-21-propeller-deicing-electrical-circuit-protection","history":"/api/acts/ad-tb20-21-propeller-deicing-electrical-circuit-protection/history","analysis":"/api/acts/ad-tb20-21-propeller-deicing-electrical-circuit-protection/analysis","conflicts":"/api/acts/ad-tb20-21-propeller-deicing-electrical-circuit-protection/conflicts","importantCases":"/api/acts/ad-tb20-21-propeller-deicing-electrical-circuit-protection/important-cases","documents":"/api/acts/ad-tb20-21-propeller-deicing-electrical-circuit-protection/documents"}}