{"id":"F2006B04632","name":"AD/BELL 407/19 - Tail Rotor Gearbox","slug":"ad-bell-407-19-tail-rotor-gearbox","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44384,"registerId":"commonwealth-F2006B04632-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\n![](image.001.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.\n\nBell Helicopter Textron Canada (BHTC) 407 Series Helicopters","sortOrder":0},{"sectionNumber":"AD/BELL 407/19 Tail Rotor Gearbox 5/2002","sectionType":"part","heading":"AD/BELL 407/19 Tail Rotor Gearbox 5/2002","content":"# AD/BELL 407/19 Tail Rotor Gearbox 5/2002\n\nApplicability: Bell Helicopter Textron Canada (BHTC) Model 407 Helicopters.\n\nRequirement: Remove the tail rotor gearbox and carry out re-installation as per Part 1 of BHTC Alert Service Bulletin (ASB) 407-97-14 Revision C.\n\nNote 1: Canadian AD CF-1998-09 R1 refers.\n\nCompliance: Unless previously accomplished, within 300 hours since the last 300 hour inspection, but no later than 27 December 2002.\n\nNote 2: Helicopter S/N 53505 and subsequent may have been completed at manufacture.\n\nThis Airworthiness Directive becomes effective on 16 May 2002.\n\nBackground: The nuts that attach the tail rotor gearbox to the tailboom have been found loose. It is believed to be an installation issue. BHTC has developed a new procedure for installation with a specific torque check procedure. The new procedure supersedes that detailed in the original issue of ASB 407-97-14. AD/BELL/407/4 has been cancelled.\n\n![](image.002.png)  \n\nEugene Paul Holzapfel\n\nDelegate of the Civil Aviation Safety Authority 7 April 2002\n\n![](image.001.png)","sortOrder":1}],"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"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This AD maintains its original narrow scope: addressing a specific mechanical installation defect in Bell 407 helicopters. It replaces an earlier AD on the same issue with an improved procedure, but does not expand beyond the original safety purpose."},"complexity_factors":["Single, specific mechanical action required (remove and reinstall one component)","Only one defined term of note ('ASB' - Alert Service Bulletin, explained in context)","Simple compliance deadline structure (hours-based OR calendar date, whichever is earlier)","No nested exceptions or conditional logic — only one exemption noted (factory-completed aircraft)","Short document (approximately 250 words)","Single cross-reference to Canadian aviation regulation (CF-1998-09 R1) and one cancelled AD"],"plain_english_summary":"This safety order requires Bell 407 owners/operators to remove and reinstall the tail rotor gearbox using a revised Bell Helicopter procedure because nuts have been found to loosen, risking in‑flight loss of control. Compliance is required within 300 flight hours or by 27 December 2002, whichever comes first.\n\nIt replaces the earlier AD/BELL/407/4; some helicopters (S/N 53505 and above) may already have the fix."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The directive refines and enforces an updated installation procedure for the same technical problem (loose tail-rotor gearbox attachment nuts) and does not materially expand the population of aircraft affected or add new kinds of obligations. It replaces an earlier AD and mandates the manufacturer’s revised procedure, so the scope remains corrective and narrowly focused on the original airworthiness issue rather than growing beyond that purpose."},"complexity_factors":["Short document (single-page style AD) with limited provisions","One main required action (remove and re-install gearbox per ASB Revision C)","Two-condition compliance deadline (within 300 hours since last 300‑hour inspection AND no later than 27 Dec 2002)","Three cross-references (BHTC ASB 407-97-14 Rev C, Canadian AD CF-1998-09 R1, prior AD/BELL/407/4 cancelled)","One limited exception/clarification (helicopter S/N 53505 and subsequent may already comply)","No extensive defined-terms or nested exceptions"],"plain_english_summary":"**What this directive does (mechanics)\n\n- Applies to: Bell Helicopter Textron Canada (BHTC) Model 407 helicopters. (Applicability)\n- Action required: Remove the tail-rotor gearbox and re-install it following Part 1 of BHTC Alert Service Bulletin (ASB) 407-97-14 Revision C. (Requirement)\n- When to do it: If not already done, complete the action within 300 flight hours after the last 300‑hour inspection, and in any case no later than 27 December 2002. (Compliance)\n- Effective date: 16 May 2002. The directive cancels the earlier AD/BELL/407/4 and relies on a revised manufacturer procedure. (Background)\n\nWhy the change was issued (stated reason)\n\n- The tail-rotor gearbox attachment nuts were found loose; the manufacturer concluded this is an installation issue and issued a revised installation procedure with a specific torque-check step. The AD directs operators to use that revised procedure (ASB Revision C). (Background)\n\nWho is affected and who pays\n\n- Affected parties: Operators/owners of BHTC Model 407 helicopters not already modified per the ASB. Aircraft with serial number 53505 and later may already have the revised procedure done at manufacture. (Note 2)\n- Who decides: The Civil Aviation Safety Authority (CASA) delegate has issued the mandatory requirement; the manufacturer (BHTC) provides the technical procedure (ASB Revision C). (front matter; Requirement)\n- Who pays: The helicopter operator pays for the removal, re-installation and inspection labour, any parts or maintenance facility costs, and aircraft downtime while maintenance is performed.\n\nPractical effects and behaviour change\n\n- Maintenance action required: Licensed maintenance personnel must remove the tail-rotor gearbox and re-install it using the specified ASB procedure, including the torque check. That replaces the prior installation method. (Requirement)\n- Operational effect: Affected helicopters will incur maintenance time and likely grounding for the duration of the work. Operators must schedule the work within the stated compliance window. (Compliance)\n\nTrade-offs, costs, incentives and implementation risks\n\n- Direct costs: labour, possible parts replacement, and aircraft downtime. The AD does not specify hours or dollar amounts; those depend on operator labour rates and whether the work is done in-house or by a third-party maintenance provider.\n- Incentives: Operators are legally required to comply; non-compliance risks regulator enforcement and continued airworthiness risk from loose attachment nuts.\n- Implementation risk: Availability of qualified maintenance personnel or authorised service centres could affect how quickly operators can comply. If the ASB requires special tooling or calibration (the ASB is referenced but not reproduced), that may add cost or delay.\n- Substitution: The AD requires the ASB procedure; operators may only use an alternative method if it is acceptable to CASA or otherwise approved under the airworthiness rules (the AD itself prescribes the ASB method). (Requirement)\n\nConcentrated benefits vs diffuse costs\n\n- Concentrated benefit: Reduced risk of gearbox detachment or related failures benefits the operator, crew and passengers of each modified helicopter directly. The safety benefit is concentrated on affected aircraft.\n- Diffuse cost: Costs are distributed across all affected operators, which may be a small, identifiable group (Model 407 fleet operators).\n\nScope and scope change (mechanical comparison to earlier steps)\n\n- The AD updates the required installation procedure by referencing ASB 407-97-14 Revision C and cancels the prior AD for the same model. It does not expand the type of aircraft affected beyond Model 407 or impose ongoing inspection regimes; it replaces the installation procedure to correct an installation defect. (Requirement; Background)\n\nTechnical references cited in the directive\n\n- BHTC Alert Service Bulletin 407-97-14 Revision C (specified installation procedure).\n- Canadian AD CF-1998-09 R1 is noted as related guidance. (Note 1)\n\nSource sections cited: Applicability, Requirement, Compliance, Notes, Background.\n"}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-407-19-tail-rotor-gearbox","history":"/api/acts/ad-bell-407-19-tail-rotor-gearbox/history","analysis":"/api/acts/ad-bell-407-19-tail-rotor-gearbox/analysis","conflicts":"/api/acts/ad-bell-407-19-tail-rotor-gearbox/conflicts","importantCases":"/api/acts/ad-bell-407-19-tail-rotor-gearbox/important-cases","documents":"/api/acts/ad-bell-407-19-tail-rotor-gearbox/documents"}}