{"id":"F2006B04637","name":"AD/BELL 407/24 - Tail Rotor Gearbox","slug":"ad-bell-407-24-tail-rotor-gearbox","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44389,"registerId":"commonwealth-F2006B04637-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.001.png)  \n\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 CASR 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.\n\n![](image.001.png)  \n\nBell Helicopter Textron Canada (BHTC) 407 Series Helicopters","sortOrder":0},{"sectionNumber":"AD/BELL 407/24 Tail Rotor Gearbox 11/200","sectionType":"part","heading":"AD/BELL 407/24 Tail Rotor Gearbox 11/2003","content":"# AD/BELL 407/24 Tail Rotor Gearbox 11/2003\n\nApplicability: Bell Helicopter Textron Canada Model 407 Helicopters serial number (S/N) 53000 through 53498, 53500 through 53522, 53524 and 53526, equipped with tail rotor gearbox case part number (P/N) 406-040-406-109 or 406-040-406-113.\n\nRequirement: 1. Identify the tail rotor gearbox case installed on the helicopter and, if applicable, check for the presence of oil feed gallery in accordance with the Accomplishment Instructions, Part I of ASB 407-03-57 Rev B.\n\n    2. If the oil feed gallery is present, re-identify the case assembly in accordance with the Accomplishment Instructions, Part I of ASB 407-03-57 Rev B.\n\n    3. If the oil feed gallery is not present create an oil feed gallery and re-identify the case in accordance with the Accomplishment Instructions, Part II of ASB 407-03- 57 Rev. B.\n\nNote: Transport Canada CF-2003-10 refers.\n\nCompliance: Tail Rotor Gearboxes installed in an aircraft:\n\nFor Requirement 1: Within 50 flight hours or 30 days from the effective date of this Directive, whichever occurs first.\n\nFor Requirement 2: Within 50 flight hours or 30 days from the effective date of this Directive, whichever occurs first.\n\nFor Requirement 3: For tail rotor gearboxes with less than 1800 flight hours time since new; prior to reaching 1800 flight hours time since new.\n\nFor tail rotor gearboxes with less than 1800 flight hours since last overhaul; prior to reaching 1800 flight hours since overhaul.\n\nFor tail rotor gearboxes with more than 1800 flight hours time since new; within 50 flight hours or 30 days from the effective date of this Directive.\n\nFor tail rotor gearboxes with more than 1800 flight hours time since last overhaul; within 50 flight hours or 30 days from the effective date of this Directive.","sortOrder":1},{"sectionNumber":"Bell Helicopter Textron Canada (BHTC) 40","sectionType":"part","heading":"Bell Helicopter Textron Canada (BHTC) 407 Series Helicopters","content":"## Bell Helicopter Textron Canada (BHTC) 407 Series Helicopters\n\nAD/BELL 407/24 (continued)","sortOrder":2},{"sectionNumber":"Tail Rotor Gearboxes held as spares:","sectionType":"part","heading":"Tail Rotor Gearboxes held as spares:","content":"## Tail Rotor Gearboxes held as spares:\n\nFor Requirements 1, 2 and 3: Prior to installation in a helicopter. This Airworthiness Directive becomes effective on 30 October 2003.\n\nBackground: There have been a number of tail rotor gearboxes identified as not having the required oil feed gallery to the duplex bearing. This reduces the oil supply to the bearing that could lead to failure of the duplex bearing. The splash lubrication the bearing receives will be sufficient to maintain the integrity of the bearing before modification of the tail rotor gearbox is required as detailed in this Directive.\n\n![](image.002.png)  \n\nJim Coyne\n\nDelegate of the Civil Aviation Safety Authority 19 September 2003\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 8 October 2003.","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"The directive's scope is limited to the listed Bell 407 serial numbers and two gearbox case P/Ns and prescribes inspection, re‑identification or modification and specific compliance windows. The text contains no indication that the applicability or required actions were expanded or narrowed from the directive as issued; it implements the corrective action described (Applicability; Requirement; Compliance)."},"complexity_factors":["Technical modification and shop work required to create an oil feed gallery and re‑identification per BHTC ASB 407‑03‑57 Rev B (Requirement 1–3; Requirement section).","Specific applicability limited to certain serial numbers and two gearbox case part numbers, requiring careful fleet/parts checks (Applicability).","Multiple, conditional compliance deadlines based on time‑in‑service and time‑since‑overhaul (Compliance: <1800 hrs vs >1800 hrs; hours vs days).","Spare gearbox treatment: mandatory compliance prior to installation, adding inventory management and pre‑installation inspection (Tail Rotor Gearboxes held as spares).","Recordkeeping and re‑identification obligations after inspection/modification (Requirement 2 and 3).","Cross‑reference to foreign regulator action may affect interpretation and sourcing of technical instructions (Note: Transport Canada CF‑2003‑10; Background)."],"plain_english_summary":"Requires operators and maintenance organisations of Bell 407 helicopters with specified tail rotor gearbox case part and serial numbers to inspect the gearbox case for an oil feed gallery and then either re‑identify the case or create the gallery and re‑identify it, following BHTC Service Bulletin ASB 407‑03‑57 Rev B. Owners/operators pay for the inspection/modification and must comply within the stated flight‑hour or day limits (including before installing spares) because missing galleries can reduce lubrication to the duplex bearing and risk bearing failure."},"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"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This AD maintains its original narrow scope — addressing a specific manufacturing defect in specific Bell 407 helicopter tail rotor gearboxes. The document does not show evidence of scope creep beyond the original safety purpose."},"complexity_factors":["Multiple serial number ranges and specific part numbers create fragmented applicability","Nested compliance deadlines based on flight hours vs. calendar time vs. overhaul status","Cross-reference to external technical document (ASB 407-03-57 Rev B) without reproducing its contents","Different compliance rules for installed gearboxes vs. spare parts","Conditional logic: three different requirement paths depending on inspection findings"],"plain_english_summary":"This CASA Airworthiness Directive requires operators of certain Bell 407s (specific serial ranges and tail-rotor gearbox part numbers) to inspect and, if needed, machine an oil feed gallery in the tail-rotor gearbox or re‑label compliant cases. A missing oil feed gallery can allow bearing failure and loss of directional control. Inspections, corrective work, and fixes to spares are time‑critical (short flight‑hour/time limits) to prevent potential catastrophic failure."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-407-24-tail-rotor-gearbox","history":"/api/acts/ad-bell-407-24-tail-rotor-gearbox/history","analysis":"/api/acts/ad-bell-407-24-tail-rotor-gearbox/analysis","conflicts":"/api/acts/ad-bell-407-24-tail-rotor-gearbox/conflicts","importantCases":"/api/acts/ad-bell-407-24-tail-rotor-gearbox/important-cases","documents":"/api/acts/ad-bell-407-24-tail-rotor-gearbox/documents"}}