{"id":"F2006B04634","name":"AD/BELL 407/20 Amdt 1 - Tailboom Tail Rotor Gearbox Support Casting","slug":"ad-bell-407-20-amdt-1-tailboom-tail-rotor-gearbox-support-casting","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44386,"registerId":"commonwealth-F2006B04634-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BELL 407/20 Amdt 1 - Tailboom Tail Rotor Gearbox Support Casting","content":"![](image.001.png)\n\n![](image.001.png)  \nAIRWORTHINESS DIRECTIVE\n\nFor the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/BELL 407/20 and issues the following 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.\n\n![](image.001.png)\n\nBell Helicopter Textron Canada (BHTC) 407 Series Helicopters\n\nAD/BELL 407/20\n\nAmdt 1\n\n  \n\nTailboom Tail Rotor Gearbox Support Casting\n\n  \n11/2002\n\nApplicability: Model 407 helicopters, serial numbers 53000 through 53475; equipped with tailboom assemblies part number 407-030-801-105, \\-107, or 407-530-014-103, identified as serial numbers 53390 through 53440, 53449, BP921, BP1014, and subcomponent tail rotor gearbox support casting part number 406-030-121-105, identified as serial numbers 980867/01-2, \\-3, \\-4, \\-5, \\-8, \\-9, \\-10.\n\nRequirement: 1. Determine if the affected part is installed on the applicable aircraft by conducting Part I of Alert Service Bulletin 407-02-53, dated 5 June 2002.\n\n    2. If an affected casting is identified by Requirement 1, perform an inspection of the casting for cracks in accordance with Part II of Alert Service Bulletin 407-02-53; and, if a crack is found, replace the tailboom before further flight.\n    3. Remove the tailboom from service until the affected tail rotor gearbox support casting is replaced.\n\nNote: Transport Canada AD CF-2002-32R1 refers.\n\nCompliance: 1. Within 10 hours time in service or 7 days after 7 August 2002, whichever occurs first.\n\n    2. Before further flight. Thereafter at intervals not to exceed 25 hours time in service.\n    3. Before 1 October 2002.\n\nThe compliance times remain unchanged by this issue. This Amendment becomes effective on 31 October 2002.\n\nBackground: Transport Canada received a report of a cracked tail rotor gearbox support casting that is part of the tailboom assembly. Investigation revealed the crack originated from a weld repair made during fabrication of the part.\n\nBell Helicopter Textron Canada (BHTC) 407 Series Helicopters\n\nAD/BELL 407/20 Amdt 1 (Continued)\n\nAmendment 1 is issued in response to a revision of the related Transport Canada AD which corrects the issue date of the Requirement document.\n\nThe original issue of this Airworthiness Directive became effective on 9 October 2002.\n\n![](image.002.jpeg)  \n\nDavid Alan Villiers\n\nDelegate of the Civil Aviation Safety Authority 12 September 2002\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 9 October 2002.","sortOrder":0}],"analysis":{"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 amendment corrects the issue date of the Requirement document only. Applicability, inspection/replacement obligations and compliance times remain unchanged."},"complexity_factors":["Technical specificity: exact helicopter model, multiple part numbers and a narrow range of serial numbers are listed (Applicability).","External-document dependence: inspections and actions must follow Alert Service Bulletin 407-02-53 Parts I and II (Requirement).","Cross-jurisdiction reference: AD refers to and aligns with a Transport Canada AD (Note / Background).","Operational deadlines: short compliance windows (10 hours or 7 days; before further flight; recurrent 25‑hour intervals; removal by 1 Oct 2002) create scheduling pressure (Compliance).","Operational impact: removal from service until replacement imposes direct downtime and replacement cost on owners/operators (Requirement 3).","Regulatory formality: CASA delegate revokes and reissues the AD; amendment only corrects a document date, not substantive measures (Intro / Background)."],"plain_english_summary":"This Airworthiness Directive replaces an earlier AD and requires operators of specific Bell 407 helicopters to check whether certain tailboom tail-rotor gearbox support castings are installed and to inspect them for cracks. If a crack is found the tailboom must be replaced or removed from service until the casting is replaced. The amendment corrects the issue date of the referenced service document; Transport Canada reported cracks originating from a weld repair."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is Amendment 1 to an existing Airworthiness Directive. The amendment explicitly states it only corrects the issue date of the referenced Requirement document (the Alert Service Bulletin). The compliance times, applicability, and safety actions remain unchanged from the original AD. The scope has not expanded beyond the original safety purpose of addressing the cracked tail rotor gearbox support casting defect."},"complexity_factors":["Multiple nested applicability conditions (aircraft serial numbers AND specific tailboom part numbers AND specific casting serial numbers)","Three distinct compliance deadlines with different triggers (hours-based, calendar-based, and absolute date)","Cross-reference to external technical document (Alert Service Bulletin 407-02-53) which is not reproduced in the AD itself","Reference to related Canadian aviation directive (Transport Canada AD CF-2002-32R1)","Conditional logic: different actions required depending on inspection results (if found, if crack found, etc.)"],"plain_english_summary":"This CASA safety order targets a manufacturing defect in the tailboom of specific Bell 407 helicopters (S/N 53000–53475) where a cracked tail rotor gearbox support casting can cause tail-rotor loss and catastrophic control failure. Owners must check for the affected casting, inspect regularly, and replace the tailboom immediately if cracks are found; helicopters with the casting must be removed from service by 1 October 2002. The amendment only corrects a reference date; the safety requirements are unchanged."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-407-20-amdt-1-tailboom-tail-rotor-gearbox-support-casting","history":"/api/acts/ad-bell-407-20-amdt-1-tailboom-tail-rotor-gearbox-support-casting/history","analysis":"/api/acts/ad-bell-407-20-amdt-1-tailboom-tail-rotor-gearbox-support-casting/analysis","conflicts":"/api/acts/ad-bell-407-20-amdt-1-tailboom-tail-rotor-gearbox-support-casting/conflicts","importantCases":"/api/acts/ad-bell-407-20-amdt-1-tailboom-tail-rotor-gearbox-support-casting/important-cases","documents":"/api/acts/ad-bell-407-20-amdt-1-tailboom-tail-rotor-gearbox-support-casting/documents"}}