{"id":"F2006B09576","name":"AD/ENST 28/20 - Mixture Control System Maintenance Checks and Modification","slug":"ad-enst-28-20-mixture-control-system-maintenance-checks-and-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54263,"registerId":"commonwealth-F2006B09576-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/ENST 28/20 - Mixture Control System Maintenance Checks and Modification","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)  Enstrom F-28 Series Helicopters\n\n \n\nAD/ENST 28/20 Mixture Control System Maintenance\n\nChecks and Modification\n\nApplicability: All models F28C and 280C.\n\n \n\nDocument: 1. Enstrom Service Directive Bulletin No. 0045; or 2. FAA AD No 77-25-05.\n\nCompliance: As per Requirement document No. 1.\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\n\n3/78\n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The provided text contains no indication that the scope of the directive was altered from its original intent. It plainly applies to all Enstrom F28C and 280C helicopters and directs compliance with the listed requirement document (Enstrom Service Directive Bulletin No. 0045 or FAA AD No 77-25-05). (Applicability; Document; Compliance.)"},"complexity_factors":["Narrow applicability limited to two helicopter model types (Applicability: All models F28C and 280C).","Relies on external requirement documents for technical detail (Document: Enstrom Service Directive Bulletin No. 0045; FAA AD No 77-25-05).","Compliance instruction delegates timing and procedural detail to the referenced document rather than setting them in the AD itself (Compliance: As per Requirement document No. 1).","Regulatory context is clear (issued under Civil Aviation Safety Authority, Schedule of Airworthiness Directives), reducing legal ambiguity about authority but concentrating technical detail elsewhere."],"plain_english_summary":"What this instrument does (mechanically)\n\n- This is an airworthiness directive issued under the Commonwealth Civil Aviation Regulations (Schedule of Airworthiness Directives). It requires maintenance checks and a modification of the mixture control system for specified Enstrom helicopters. (COMMONWEALTH OF AUSTRALIA — PART 39 — CIVIL AVIATION SAFETY AUTHORITY; AD/ENST 28/20)\n\nWho it affects\n\n- Owners and operators of all Enstrom F-28C and 280C helicopters. (Applicability: All models F28C and 280C)\n\nWhich technical instructions you must follow\n\n- The work must be done in accordance with one of the listed requirement documents: either Enstrom Service Directive Bulletin No. 0045, or FAA AD No 77-25-05. The AD states compliance is “As per Requirement document No. 1.” (Document: 1. Enstrom Service Directive Bulletin No. 0045; or 2. FAA AD No 77-25-05. Compliance: As per Requirement document No. 1.)\n\nWho decides and who pays\n\n- The regulator named on the instrument (Civil Aviation Safety Authority) issues the directive and specifies the requirement document. (COMMONWEALTH OF AUSTRALIA — PART 39 — CIVIL AVIATION SAFETY AUTHORITY)\n- The people who will directly pay for and arrange the required work are the helicopter owners/operators (they must arrange maintenance and modification to meet the AD’s requirements). (Applicability; Compliance)\n\nWhat behaviour changes\n\n- Operators must arrange and carry out the specified maintenance checks and the modification set out in the referenced requirement document. This will change operator behaviour by adding required maintenance tasks and scheduling those tasks in fleet operations. (Document; Compliance)\n\nPractical trade-offs, costs, and implementation points to watch\n\n- Compliance burden: The directive imposes a maintenance and modification obligation. That typically requires labour, possibly parts, and aircraft downtime while the work is performed. The AD itself points to an external technical document for the exact steps and timing, so the immediate legal obligation is to follow that document. (Document; Compliance)\n- Incentives and who bears costs: Owners/operators bear the financial and operational cost of meeting the directive; the AD imposes an obligation rather than providing funding or implementation services. (Applicability; Compliance)\n- Implementation risk and discretion: Technical detail and accepted methods are supplied by the referenced service/FAA documents; the regulator’s role is to require compliance with those documents. This structure concentrates technical discretion into the referenced documents and the maintenance personnel who execute them. (Document)\n- Opportunity costs: Time and money spent on these mandated checks/modification cannot be used for other maintenance or operational priorities until completed. (Compliance)\n- Substitution effects: Because the AD points to a specific service bulletin or FAA AD, operators will follow those documents’ procedures rather than alternative procedures unless those alternatives are approved under the regulator’s usual approvals process (not detailed in this text). (Document)\n\nHow to comply (mechanically)\n\n- Identify affected helicopters (all F28C and 280C). (Applicability)\n- Obtain and follow the steps and timing in the chosen requirement document (Enstrom Service Directive Bulletin No. 0045 or FAA AD No 77-25-05). (Document; Compliance)\n\nSource references (from the instrument)\n\n- Applicability: All models F28C and 280C.\n- Document: 1. Enstrom Service Directive Bulletin No. 0045; or 2. FAA AD No 77-25-05.\n- Compliance: As per Requirement document No. 1.\n- Issuing context: Commonwealth of Australia — Civil Aviation Regulations 1998, Part 39 — Civil Aviation Safety Authority, Schedule of Airworthiness Directives.\n"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a standard Airworthiness Directive with narrow, specific scope addressing a particular maintenance issue on specific helicopter models. It has not expanded beyond its original safety purpose."},"complexity_factors":["Very short document (approximately 150 words of substantive content)","Only 2 defined applicability criteria (F28C and 280C models)","Simple compliance structure: 'follow the service bulletin'","No nested exceptions, conditional logic, or cross-references to other legislation","Single requirement with alternative compliance path (FAA AD as acceptable alternative)","No interpretation section or defined terms"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** issued by Australia's Civil Aviation Safety Authority (CASA) that mandates specific maintenance and modifications for **Enstrom F-28 series helicopters** (specifically the F28C and 280C models).\n\n**What it does:**\n- Requires owners and operators of these helicopters to perform **maintenance checks and modifications** on the **mixture control system** — the mechanism that regulates the fuel-air mixture going to the engine.\n- Operators must follow the procedures set out in **Enstrom Service Directive Bulletin No. 0045** (or alternatively, the US Federal Aviation Administration's AD 77-25-05).\n\n**Who it affects:**\n- Owners and operators of **Enstrom F28C and 280C helicopters**.\n- Licensed aircraft maintenance engineers who work on these aircraft.\n\n**Why it matters:**\n- The mixture control system is critical for safe engine operation. Faults in this system could cause **engine failure or power loss** — extremely dangerous in a helicopter.\n- This directive ensures a known safety issue is addressed before it causes an accident. Compliance is **legally mandatory** — you cannot legally fly the aircraft until the work is done."}},"importantCases":[],"_links":{"self":"/api/acts/ad-enst-28-20-mixture-control-system-maintenance-checks-and-modification","history":"/api/acts/ad-enst-28-20-mixture-control-system-maintenance-checks-and-modification/history","analysis":"/api/acts/ad-enst-28-20-mixture-control-system-maintenance-checks-and-modification/analysis","conflicts":"/api/acts/ad-enst-28-20-mixture-control-system-maintenance-checks-and-modification/conflicts","importantCases":"/api/acts/ad-enst-28-20-mixture-control-system-maintenance-checks-and-modification/important-cases","documents":"/api/acts/ad-enst-28-20-mixture-control-system-maintenance-checks-and-modification/documents"}}