{"id":"F2006B04529","name":"AD/BELL 206/77 - Tail Rotor Drive Shaft - Replacement of Bearing Hangars","slug":"ad-bell-206-77-tail-rotor-drive-shaft-replacement-of-bearing-hangars","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":114242,"registerId":"commonwealth-F2006B04529-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BELL 206/77 - Tail Rotor Drive Shaft - Replacement of Bearing Hangars","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\nBell Helicopter Textron Canada (BHTC) 206 and Agusta Bell 206 Series Helicopters\n\n \n\nAD/BELL 206/77 Tail Rotor Drive Shaft - Replacement\n\nof Bearing Hangars\n\n\n12/78\n\n \n\nApplicability: Models 206A, 206B, AB206 & AB206B with S/Nos. as per Requirement Doc’s. Document:               1. Bell SB No. 206-77-9; or\n\n2.    FAA AD 78-16-01 Amendment 39-3271; or\n\n \n\n3.    Agusta SB No. BT206-123.\n\n \n\nCompliance: No later than the next scheduled 1200 hourly inspection completed after 31 January 1979.\n\n \n\nBackground: AD/Agusta 206/61 equivalent.\n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The text indicates the directive is equivalent to a prior Agusta AD (Background) and specifies replacement of bearing hangars only for listed 206 variants and serial numbers (Applicability). The document does not state any expansion or narrowing beyond that equivalence; therefore there is no clear change of scope from the prior referenced action within the supplied text."},"complexity_factors":["Narrow applicability limited to specific 206 model variants and serial numbers (Applicability).","Requirement to follow one of three external technical documents (Bell SB 206-77-9, FAA AD 78-16-01, Agusta SB BT206-123) creates dependency on referenced material (Document list).","Fixed compliance timing tied to the next scheduled 1200‑hour inspection after a historical date requires operators to map directive timing onto individual maintenance schedules (Compliance).","Administrative task to verify affected serial numbers against the requirement documents can add operational overhead (Applicability).","The directive is procedural (replace part) rather than prescriptive about who performs the work, leaving implementation details to operators and maintenance providers (Document list)."],"plain_english_summary":"What the directive requires (mechanics)\n\n- The document is an airworthiness directive issued under the Commonwealth Civil Aviation Regulations that mandates replacement of the tail rotor drive shaft bearing hangars on certain Bell/Agusta 206 series helicopters (see header and Applicability).\n- The replacement must be carried out in accordance with one of three referenced technical documents: Bell Service Bulletin (SB) No. 206-77-9, FAA AD 78-16-01 (Amendment 39-3271), or Agusta SB No. BT206-123 (see Document list under Applicability).\n- The deadline for compliance is the next scheduled 1200‑hour inspection completed after 31 January 1979 (Compliance).\n\nWho this affects\n\n- Owners and operators of Bell 206A, 206B, AB206 and AB206B helicopters that are listed by serial number in the referenced requirement documents (Applicability).\n- Maintenance organisations and technicians that perform the replacement work under the referenced service bulletins or FAA AD (Document list).\n\nWhy it matters (stated purpose and practical implications)\n\n- The directive’s stated action is replacement of bearing hangars on the tail rotor drive shaft (title and Document list). The background notes it is equivalent to an earlier Agusta directive (Background).\n- Practically, the directive imposes a one‑time maintenance task on affected aircraft within a specified inspection interval. That creates immediate labour and parts costs for operators, an administrative task to confirm serial‑number applicability, and a demand for maintenance capacity to do the work (Applicability; Compliance).\n\nCosts, incentives and trade‑offs (testing the stated purpose against practical consequences)\n\n- Who pays: aircraft owners/operators are the parties who must arrange and fund the replacement work (Applicability; Compliance). The directive does not allocate funding or subsidies.\n- Who decides and enforces: the Civil Aviation Safety Authority issues the directive under the Part 39 airworthiness regime; compliance is mandatory for affected aircraft (header). The directive points operators to the technical documents that define the exact replacement procedure (Document list).\n- Compliance burden: operators must (a) check serial numbers against the requirement documents to determine if their helicopter is affected (Applicability), (b) schedule the replacement by the next 1200‑hour inspection after the specified date (Compliance), and (c) follow the referenced SB/AD procedures when performing the work (Document list). Administrative and labour time are the main compliance costs.\n- Market effects and incentives: the directive increases short‑term demand for replacement parts and maintenance labour for affected models (Applicability; Document list). Independent maintenance providers able to perform work to the referenced SBs/AD may capture that demand, subject to normal market competition. The directive constrains operator choice in that the replacement must be completed to the specified standards and by the stated deadline (Compliance; Document list).\n- Implementation risks and opportunity costs: effective compliance depends on availability of the referenced technical documents and the required parts; delays in parts or qualified labour could force scheduling shifts for affected operators. Time and money spent on this mandated maintenance cannot be applied elsewhere during the same period (Applicability; Compliance).\n\nOther notes\n\n- The directive lists three alternate technical references; following any one of them appears to satisfy the requirement (Document list). That gives operators mechanical guidance options but does not change the mandatory nature or the deadline of the AD (Applicability; Compliance).\n- The text identifies the AD as equivalent to a prior Agusta AD, which indicates alignment with previous regulatory action rather than a different technical scope (Background).\n\nSource citations: header (authority), Applicability, Document list, Compliance, Background."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound maintenance directive issued in 1978. It has not grown beyond its original purpose of mandating a specific safety repair on specific helicopter models. The scope remains tightly focused on the tail rotor drive shaft bearing hangar replacement."},"complexity_factors":["Very short document (approximately 150 words)","Only 4 defined model categories and 3 reference documents","Single, clear compliance action (replacement of bearing hangars)","Single, straightforward deadline (next 1200-hour inspection after fixed date)","No nested exceptions, conditional logic, or cross-references to other legislation","No interpretation section or defined terms"],"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). Think of it as a \"recall notice\" for aircraft, but legally binding.\n\n**What it requires:** Owners and operators of specific Bell and Agusta-Bell helicopter models must **replace the bearing hangars** (support brackets that hold bearings) on the tail rotor drive shaft. The tail rotor drive shaft is the mechanical component that transfers power to the tail rotor — the small vertical rotor that stops the helicopter from spinning uncontrollably.\n\n**Which helicopters are affected:**\n- Bell 206A and 206B models\n- Agusta-Bell AB206 and AB206B models\n- Only those with specific serial numbers listed in the referenced technical documents\n\n**When it must be done:** By the next scheduled 1,200-hour inspection after 31 January 1979. (Helicopters are inspected based on flight hours, not calendar time — so this is a \"flying hours\" deadline.)\n\n**Why it matters:** Faulty bearing hangars could cause the tail rotor drive shaft to fail. If that happens, the pilot loses control of the helicopter's yaw (directional control), which can be catastrophic.\n\n**How to comply:** Follow one of these technical documents:\n- Bell Service Bulletin 206-77-9, or\n- FAA Airworthiness Directive 78-16-01, or  \n- Agusta Service Bulletin BT206-123\n\n**Background note:** This directive replaces or is equivalent to an earlier directive called AD/Agusta 206/61."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-206-77-tail-rotor-drive-shaft-replacement-of-bearing-hangars","history":"/api/acts/ad-bell-206-77-tail-rotor-drive-shaft-replacement-of-bearing-hangars/history","analysis":"/api/acts/ad-bell-206-77-tail-rotor-drive-shaft-replacement-of-bearing-hangars/analysis","conflicts":"/api/acts/ad-bell-206-77-tail-rotor-drive-shaft-replacement-of-bearing-hangars/conflicts","importantCases":"/api/acts/ad-bell-206-77-tail-rotor-drive-shaft-replacement-of-bearing-hangars/important-cases","documents":"/api/acts/ad-bell-206-77-tail-rotor-drive-shaft-replacement-of-bearing-hangars/documents"}}