{"id":"F2006B09568","name":"AD/ENST 28/13 - Main Rotor Hub Retention Lock Washer - Replacement","slug":"ad-enst-28-13-main-rotor-hub-retention-lock-washer-replacement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54237,"registerId":"commonwealth-F2006B09568-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/ENST 28/13 - Main Rotor Hub Retention Lock Washer - Replacement","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 28/13 Main Rotor Hub Retention Lock\n\nWasher - Replacement\n\n\n4/76\n\n \n\nApplicability: All models F-28A with S/Nos. 4 to 275, 277, 278, 280 to 283, and models 280 with\n\nS/Nos. 1001 to 1006.\n\n \n\nDocument: 1. Enstrom Service Note No. 0025A; or 2. FAA AD 75-22-10.\n\nCompliance: Within 25 hours time in service after 30 April 1976.\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":{"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The text provided sets a specific corrective requirement for a defined set of serial numbers and does not indicate any expansion or contraction of scope relative to its stated action. There is no material in the instrument showing a change from an earlier or different intent; the directive confines action to replacement of the specified washer using the referenced service documents within the stated compliance window. (AD/ENST 28/13; Applicability; Document; Compliance)"},"complexity_factors":["Narrow technical scope: single component (main rotor hub retention lock washer) and single action (replacement). (AD/ENST 28/13)","Limited applicability defined by specific model and serial numbers, requiring careful serial-number checking. (Applicability)","Short, specific compliance window (25 hours TIS after 30 April 1976) increases scheduling pressure. (Compliance)","Reliance on external documents (Enstrom Service Note No. 0025A or FAA AD 75-22-10) for procedural detail creates operational dependency. (Document)","Regulatory enforcement: directive is mandatory and requires operator/maintenance compliance and record-keeping to show adherence. (AD/ENST 28/13; Compliance)"],"plain_english_summary":"Owners and operators of specified Enstrom F‑28/F‑280 helicopters must replace the main rotor hub retention lock washer per Enstrom Service Note No. 0025A or FAA AD 75‑22‑10 within 25 hours TIS after 30 April 1976. Maintenance organisations and certifying engineers must perform/approve the work.\n\nThis mandatory airworthiness directive imposes direct costs and downtime on operators and ensures corrective maintenance to maintain aircraft airworthiness."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, single-issue safety directive focused on one specific mechanical defect in a narrow range of aircraft. It has not expanded beyond its original purpose of mandating a part replacement."},"complexity_factors":["Extremely short document (approximately 150 words)","Only 2 defined applicability criteria (aircraft model and serial number ranges)","Single compliance action with clear deadline","No cross-references to other legislation beyond optional technical documents","No conditional logic or exceptions","Straightforward command structure: identify aircraft → do action → by deadline"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). It requires owners and operators of specific **Enstrom F-28 series helicopters** to replace a particular part: the **main rotor hub retention lock washer**.\n\n**Who it affects:**\n- Owners and operators of Enstrom F-28A helicopters with serial numbers 4 to 275, 277, 278, and 280 to 283\n- Owners and operators of Enstrom 280 helicopters with serial numbers 1001 to 1006\n\n**What must be done:**\n- Replace the main rotor hub retention lock washer following either:\n  - Enstrom Service Note No. 0025A, **or**\n  - FAA Airworthiness Directive 75-22-10 (the equivalent US safety order)\n\n**When it must be done:**\n- Within 25 hours of flight time after 30 April 1976\n\n**Why it matters:**\nThe main rotor hub is the critical component that attaches the helicopter's rotor blades to the aircraft. A faulty retention lock washer could cause the rotor to detach in flight — a catastrophic failure. This AD ensures a known defect is fixed before it causes an accident."}},"importantCases":[],"_links":{"self":"/api/acts/ad-enst-28-13-main-rotor-hub-retention-lock-washer-replacement","history":"/api/acts/ad-enst-28-13-main-rotor-hub-retention-lock-washer-replacement/history","analysis":"/api/acts/ad-enst-28-13-main-rotor-hub-retention-lock-washer-replacement/analysis","conflicts":"/api/acts/ad-enst-28-13-main-rotor-hub-retention-lock-washer-replacement/conflicts","importantCases":"/api/acts/ad-enst-28-13-main-rotor-hub-retention-lock-washer-replacement/important-cases","documents":"/api/acts/ad-enst-28-13-main-rotor-hub-retention-lock-washer-replacement/documents"}}