{"id":"F2006B09588","name":"AD/ENST 28/31 - Main Rotor Transmission Clutch Assembly","slug":"ad-enst-28-31-main-rotor-transmission-clutch-assembly","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54294,"registerId":"commonwealth-F2006B09588-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/ENST 28/31 - Main Rotor Transmission Clutch Assembly","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 28/31 Main Rotor Transmission Clutch Assembly 5/89\n\nDM\n\nApplicability: All model F28 series helicopters equipped with P/N 28- 13401-1, Formsprag CL 40526-1 through -7 main rotor transmission clutch assembly.\n\n \n\nRequirement: Action in accordance with Enstrom Service Directive Bulletin No 0068. Additionally, for F-28F, F280F and 280FX helicopters inspect clutch assembly for part number. If clutch P/N 28- 13401-1 fitted, replace with clutch P/N 28-13401-2 before further flight.\n\n \n\nNote: FAA AD 89-04-09 refers.\n\n \n\nCompliance: At next inspection for issue of a Maintenance Release or by 31 March 1989 whichever occurs first.\n\n \n\nBackground: Failure of the 28-13401-1 clutch has resulted in severe damage to helicopters.\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, targeted safety directive addressing a specific mechanical failure in a specific helicopter series. It has not expanded beyond its original purpose of mandating clutch replacement to prevent accidents."},"complexity_factors":["Very short document (approximately 150 words of substantive content)","Only 2 defined part numbers (P/N 28-13401-1 and P/N 28-13401-2)","Single conditional requirement (if-then logic for specific models)","No cross-references to other legislation (only references external technical bulletin and FAA AD for information)","Clear, unambiguous compliance deadline","Straightforward applicability section with specific model and part number identification"],"plain_english_summary":"This CASA Airworthiness Directive orders owners/operators of Enstrom F-28 series helicopters to inspect and, where found, replace a faulty main rotor transmission clutch assembly (P/N 28-13401-1) with the improved P/N 28-13401-2 per Enstrom Service Directive Bulletin No. 0068. Affected aircraft must have the unsafe part replaced before further flight or by the next Maintenance Release inspection, or by 31 March 1989, whichever is earlier."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The instrument's scope does not indicate a change from its stated safety purpose: it applies to all F‑28 series helicopters fitted with clutch P/N 28‑13401‑1 and mandates inspection and replacement to address documented clutch failures. The text sets applicability, the required corrective action (per Enstrom Service Directive Bulletin No 0068), and a compliance timetable (Applicability; Requirement; Compliance; Background), without expanding or narrowing the described target beyond those elements."},"complexity_factors":["Narrow technical applicability to Enstrom F‑28 series with a specific clutch part number (Applicability).","Mandatory immediate operational constraint: replacement before further flight if P/N 28‑13401‑1 is fitted (Requirement).","Compliance deadline tied to either next maintenance‑release inspection or a fixed calendar date (Compliance).","Dependence on an external service document (Enstrom Service Directive Bulletin No 0068) for the required actions (Requirement).","Reference to a corresponding FAA AD increases cross‑jurisdictional compliance consideration (Note).","Safety consequence is high (documented severe damage), which raises urgency for operators and inspectors (Background).","Implementation requires qualified maintenance personnel and spare parts availability, creating potential operational downtime and cost (inference from Requirement/Compliance)."],"plain_english_summary":"*AD/ENST 28/31* requires owners/operators of Enstrom F‑28 series helicopters fitted with Formsprag main rotor clutch P/N 28‑13401‑1 to inspect per Enstrom Service Directive Bulletin No 0068 and, if that part is fitted, replace it with P/N 28‑13401‑2 before further flight. Compliance must occur at the next maintenance‑release inspection or by 31 March 1989. The directive responds to clutch failures that caused severe damage; operators pay for inspection/replacement and maintenance authorities decide airworthiness to return the helicopter to service (Applicability; Requirement; Compliance; Background)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-enst-28-31-main-rotor-transmission-clutch-assembly","history":"/api/acts/ad-enst-28-31-main-rotor-transmission-clutch-assembly/history","analysis":"/api/acts/ad-enst-28-31-main-rotor-transmission-clutch-assembly/analysis","conflicts":"/api/acts/ad-enst-28-31-main-rotor-transmission-clutch-assembly/conflicts","importantCases":"/api/acts/ad-enst-28-31-main-rotor-transmission-clutch-assembly/important-cases","documents":"/api/acts/ad-enst-28-31-main-rotor-transmission-clutch-assembly/documents"}}