{"id":"F2006B04338","name":"AD/BELL 204/35 - Tail Rotor Gearbox Duplex Bearings","slug":"ad-bell-204-35-tail-rotor-gearbox-duplex-bearings","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44153,"registerId":"commonwealth-F2006B04338-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"AIRWORTHINESS DIRECTIVE","sectionType":"part","heading":"AIRWORTHINESS DIRECTIVE","content":"# AIRWORTHINESS DIRECTIVE\n\n![](image.002.png)\n\n![](image.002.png)  \nFor the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CAR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.","sortOrder":0},{"sectionNumber":"AD/BELL 204/35 Tail Rotor Gearbox Duplex","sectionType":"part","heading":"AD/BELL 204/35 Tail Rotor Gearbox Duplex Bearings 8/2000","content":"# AD/BELL 204/35 Tail Rotor Gearbox Duplex Bearings 8/2000\n\nApplicability: Model 204B.\n\nRequirement: Remove from service tail rotor gearbox duplex bearing sets P/N 204-040-424-001 with S/Nos 1 to 182, MB183 to MB382, MB442, MB486, MB513, MB518, MB519, MB524, MB530, MB531, MB544, MB545, MB548, MB549, MB551, MB553, MB554, MB561, MB659, MB743, MB744, MB760 to MB769, and MB927 to\n\nMB936 inclusive installed in tail rotor quill P/N 204-040-012-009.\n\nNote: FAA AD 90-01-11 refers.\n\nCompliance: Before further flight after the effective date of this directive.\n\nThis Airworthiness Directive becomes effective on 10 August 2000.\n\nBackground: This directive is issued to prevent failure of the tail rotor gearbox and subsequent loss of control. It also follows the re-introduction of the AD Series after sixteen years.\n\n![](image.003.png)  \n\nDavid Alan Villiers\n\nDelegate of the Civil Aviation Safety Authority 6 July 2000\n\n![](image.002.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 12 July 2000.","sortOrder":1}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a standard single-issue airworthiness directive targeting a specific safety defect in specific aircraft. It has not expanded beyond its original purpose of addressing the tail rotor gearbox bearing failure risk."},"complexity_factors":["Very short document (under 300 words)","Only 3 operative sections: Applicability, Requirement, and Compliance","No defined terms section or interpretation provisions","No cross-references to other legislation (only a non-binding note referencing a US FAA directive)","Simple conditional logic: if you have these specific serial numbers, remove them before flying","Single exceptionless requirement with clear deadline","Straightforward list of affected serial numbers (though the list is lengthy and cut off mid-document)"],"plain_english_summary":"This CASA safety order immediately grounds Bell 204B helicopters that contain specific tail rotor gearbox bearing sets (listed part and serial numbers) until those bearings are removed. The bearings, located in the tail rotor quill, are considered unsafe and must be replaced before the next flight after 10 August 2000 to prevent tail rotor gearbox failure and potential loss of control."},"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive confines action to Model 204B and the listed bearing sets installed in tail rotor quill P/N 204-040-012-009; the text shows no alteration or expansion of that stated scope."},"complexity_factors":["Narrow technical scope: applies only to Model 204B (Applicability).","Detailed parts identification: specific P/N and an extensive list of S/Ns must be matched (Requirement).","Immediate compliance timeframe: action required 'before further flight' after effective date (Compliance).","Regulatory basis: issued under CAR 1998 subreg 39.1(1) by a CASA delegate (preamble/signature block).","Cross-reference to FAA AD 90-01-11 (Note), which may impose related tracking or verification steps.","Effective date specified (becomes effective 10 August 2000), creating a fixed compliance deadline."],"plain_english_summary":"This Airworthiness Directive requires operators of Bell Model 204B helicopters to remove specified tail‑rotor gearbox duplex bearing sets (listed by part and serial numbers) installed in tail rotor quill P/N 204-040-012-009. Removal must be carried out before any further flight from the AD’s effective date. The stated aim is to prevent tail‑rotor gearbox failure and possible loss of control."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-204-35-tail-rotor-gearbox-duplex-bearings","history":"/api/acts/ad-bell-204-35-tail-rotor-gearbox-duplex-bearings/history","analysis":"/api/acts/ad-bell-204-35-tail-rotor-gearbox-duplex-bearings/analysis","conflicts":"/api/acts/ad-bell-204-35-tail-rotor-gearbox-duplex-bearings/conflicts","importantCases":"/api/acts/ad-bell-204-35-tail-rotor-gearbox-duplex-bearings/important-cases","documents":"/api/acts/ad-bell-204-35-tail-rotor-gearbox-duplex-bearings/documents"}}