{"id":"F2006B04700","name":"AD/BELL 47/77 Amdt 1 - Tail Rotor Hub Bolts","slug":"ad-bell-47-77-amdt-1-tail-rotor-hub-bolts","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44464,"registerId":"commonwealth-F2006B04700-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BELL 47/77 Amdt 1 - Tail Rotor Hub Bolts","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)  Bell Helicopter Textron 47 (All Variants) Series Helicopters\n\n \n\nAD/BELL 47/77\n\nAmdt 1\n\n\nTail Rotor Hub Bolts 10/86\n\n \n\nApplicability: Models 47B, 47B3, 47D, 47D-1, 47G, 47G-2 and 47H-1. Document:  Bell SB No. 47-76-1. Kawasaki-Bell S.B. No. KSB-Bell 341.\n\nCompliance: Before 1 March 1976. For Kawasaki-Bell: Prior to issue of Certificate of Airworthiness.\n\n \n\nBackground: The existing tail rotor hub bolts have been subject to failure due to fatigue. This Directive has been amended to include Kawasaki- Bell Helicopters.\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":true,"description":"The Directive was amended to include Kawasaki‑Bell Helicopters in addition to the Bell models previously covered. The amendment extends the AD's applicability to Kawasaki‑Bell machines and sets a certification-linked compliance timing for those aircraft (Compliance; Background)."},"complexity_factors":["Narrow applicability: a short list of specific aircraft models (Applicability).","Single technical issue identified (tail rotor hub bolt fatigue) rather than multiple failure modes (Background).","Compliance is time-bound with a single clear deadline for Bell models and a certification-tied deadline for Kawasaki‑Bell (Compliance).","Technical execution delegated to referenced service bulletins rather than detailed in the AD itself (Document).","Regulatory amendment limited to adding Kawasaki‑Bell—no additional procedural complexity described (Background)."],"plain_english_summary":"What this instrument does, mechanically:\n\n- This Airworthiness Directive (AD) requires operators/owners of certain Bell 47 series helicopters to follow the corrective work described in the listed service bulletins for the tail rotor hub bolts. The directive cross-references Bell SB No. 47-76-1 and Kawasaki-Bell S.B. No. KSB-Bell 341 (see \"Document\"). (Document)\n- It sets fixed compliance deadlines. For the Bell models listed, the required action must be done before 1 March 1976. For Kawasaki‑Bell aircraft, the action must be done prior to issuance of a Certificate of Airworthiness. (Compliance)\n\nWho is affected:\n\n- Owners/operators of Bell Helicopter Textron 47 series: Models 47B, 47B3, 47D, 47D-1, 47G, 47G-2 and 47H-1. (Applicability)\n\nWhy the requirement exists (official claim and immediate mechanical reason):\n\n- The directive states that existing tail rotor hub bolts have experienced fatigue failures. The stated purpose is to address that failure mechanism by implementing the actions in the referenced service bulletins. (Background; Document)\n- The Directive was amended to add Kawasaki‑Bell Helicopters to the list of affected machines. (Background)\n\nWho pays, who decides, and what behavioural change is required:\n\n- Who pays: Owners/operators of the listed helicopter models will bear the direct costs of complying — parts, labour and aircraft downtime required to implement the work called up by the Bell and Kawasaki‑Bell service bulletins. (Applicability; Document; Compliance)\n- Who decides: The AD (a regulatory instrument under Part 39, Schedule of Airworthiness Directives) prescribes the obligation; the specific technical steps are set out in the referenced service bulletins. The regulator issued the amendment that expanded applicability to Kawasaki‑Bell. (Document; Background)\n- Behaviour change required: Affected operators must arrange and complete the specified inspections/repairs/modifications to tail rotor hub bolts by the stated deadlines in the AD and follow the procedures in the referenced service bulletins. (Document; Compliance)\n\nCosts, incentives and trade-offs to consider (mechanisms, not judgements):\n\n- Cost mechanics: Compliance requires procurement of specified replacement bolts or parts, certified maintenance labour, and aircraft out-of-service time. Those are direct financial and time costs to operators. (Document; Compliance)\n- Incentives: The regulatory requirement creates a compliance incentive (to meet certification and legal obligations), and an operational incentive to avoid in-service failure risk associated with fatigue. (Background; Compliance)\n- Trade-offs and opportunity cost: Funds and maintenance capacity used to comply cannot be used elsewhere (other maintenance, operations, upgrades). Operators may need to schedule downtime or substitute aircraft. (Applicability; Compliance)\n\nImplementation risk and compliance burden:\n\n- Implementation risk: Successful mitigation depends on correct execution of the steps in the referenced service bulletins and availability of parts and qualified maintenance personnel. The AD does not itself specify technical steps but relies on the service bulletins for technical detail. (Document)\n- Compliance burden: The AD creates an absolute compliance deadline. For Kawasaki‑Bell aircraft the deadline ties into the certification process (Certificate of Airworthiness). Operators must document compliance as part of airworthiness records. (Compliance)\n\nEffects on private enterprise and competition (mechanisms):\n\n- The AD applies narrowly to specific models; therefore the primary economic effect is concentrated on owners/operators of those machines. (Applicability)\n- Compliance increases marginal operating cost for those owners/operators (parts, labour, downtime). That can influence decisions about aircraft deployment, resale, or retirement, depending on each operator's economics. (Document; Compliance)\n\nScope change note:\n\n- The AD explicitly states it has been amended to include Kawasaki‑Bell Helicopters, extending the directive's reach beyond the originally listed Bell instances. (Background)\n\nPrimary cited sections: (Applicability), (Document), (Compliance), (Background)."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This amendment performs exactly what its title suggests — expanding the existing tail rotor bolt safety requirement to include Kawasaki-Bell manufactured variants. The scope remains tightly focused on the original safety purpose (preventing fatigue failures in tail rotor hub bolts) and has not grown beyond this specific mechanical issue."},"complexity_factors":["Very short document (approximately 150 words of substantive content)","Only 2 defined technical references (the service bulletin numbers)","Simple conditional structure: applicability list + compliance deadline + background","No nested exceptions or cross-references to other legislation","Single amendment purpose: adding Kawasaki-Bell to existing directive","Clear, unambiguous compliance dates with no alternative methods"],"plain_english_summary":"**What this is:** This is an Airworthiness Directive (AD) — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) under the Civil Aviation Regulations 1998.\n\n**What it does:** It requires owners and operators of specific Bell 47 series helicopters to replace or inspect their tail rotor hub bolts before a deadline. The bolts were failing due to metal fatigue (weakening from repeated stress), which could cause the tail rotor to fail and the helicopter to crash.\n\n**Who it affects:**\n- **Helicopter models:** Bell 47B, 47B3, 47D, 47D-1, 47G, 47G-2, and 47H-1\n- **Manufacturers covered:** Original Bell Helicopter Textron models AND Kawasaki-Bell variants (Japanese-built versions under license)\n\n**The safety fix:** Operators must follow the technical instructions in Bell Service Bulletin No. 47-76-1 or Kawasaki-Bell Service Bulletin No. KSB-Bell 341.\n\n**Compliance deadlines:**\n- For most helicopters: Before 1 March 1976\n- For Kawasaki-Bell helicopters: Before the helicopter can be issued a Certificate of Airworthiness (basically, before it can legally fly)\n\n**Why it matters:** Fatigue failures in tail rotor components can cause catastrophic loss of control. This directive prevents crashes by forcing replacement of defective bolts before they fail."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-47-77-amdt-1-tail-rotor-hub-bolts","history":"/api/acts/ad-bell-47-77-amdt-1-tail-rotor-hub-bolts/history","analysis":"/api/acts/ad-bell-47-77-amdt-1-tail-rotor-hub-bolts/analysis","conflicts":"/api/acts/ad-bell-47-77-amdt-1-tail-rotor-hub-bolts/conflicts","importantCases":"/api/acts/ad-bell-47-77-amdt-1-tail-rotor-hub-bolts/important-cases","documents":"/api/acts/ad-bell-47-77-amdt-1-tail-rotor-hub-bolts/documents"}}