{"id":"F2006B04693","name":"AD/BELL 47/65 - Duplex Pitch Change Bearing - Inspection and Retirement","slug":"ad-bell-47-65-duplex-pitch-change-bearing-inspection-and-retirement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44450,"registerId":"commonwealth-F2006B04693-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BELL 47/65 - Duplex Pitch Change Bearing - Inspection and Retirement","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nBell Helicopter Textron 47 (All Variants) Series Helicopters\n\nAD/BELL 47/65 Duplex Pitch Change Bearing \\- Inspection\n\nand Retirement\n\n  \n8/70\n\nApplicability: All model 47D-1, 47G, 47G-2 and 47H-1 fitted with duplex pitch change bearing P/N 47-641-131-1.\n\nRequirement: 1. Inspection: Dismantle the tail rotor drive head sufficiently to expose the duplex pitch change bearings and guide sleeve P/N 47-641-040 or 47-641-130.\n\n    1.1. Inspect the outside surface of the guide sleeve for scoring.\n\n    1.2. Inspect the duplex bearing for roughness.\n\n2. Retirement: Replace duplex pitch change bearings P/N 47-641-131-1.\n\nNote: FAA AD 70-14-1 also refers.\n\nCompliance: For Para. 1 \\- Within 100 hours time in service after 31 August 1970. For Para. 2 \\- At intervals not exceeding 600 hours total time in service.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive prescribes inspections and mandatory replacement for a specific duplex pitch change bearing on listed Bell 47 model helicopters. It does not expand applicability beyond the named models and part numbers, nor introduce additional categories of components or aircraft. The mechanical actions and timing set out (inspection within 100 hours after 31 August 1970; replacement at intervals not exceeding 600 hours) are consistent with the directive's stated remedial purpose and do not alter the original narrow scope. (Applicability; Requirement; Retirement; Compliance)"},"complexity_factors":["Narrow technical scope limited to specific helicopter models and a single bearing part number (Applicability)","Requires physical dismantling of the tail rotor drive head to access components (Requirement)","Inspection criteria are qualitative (\"scoring\", \"roughness\"), introducing subjective judgment for inspectors (Requirement 1.1, 1.2)","Fixed, rule-based replacement interval (600 hours) simplifies timing but requires tracking total time-in-service per component (Compliance Para. 2)","Historic compliance date reference (100 hours after 31 August 1970) requires operators to map the directive onto current maintenance records if still relevant (Compliance Para. 1)","Cross-reference to FAA AD adds an external source to consult for related guidance or technical background (Note)"],"plain_english_summary":"What this directive does, in plain terms:\n\n- Which aircraft it applies to: All Bell Helicopter Textron Model 47 series helicopters specifically identified as 47D-1, 47G, 47G-2 and 47H-1 when they are fitted with the duplex pitch change bearing part number 47-641-131-1. (Applicability)\n\n- Mechanical requirements:\n  - Inspect: Operators must dismantle the tail rotor drive head enough to see the duplex pitch change bearings and the guide sleeve (P/N 47-641-040 or 47-641-130). They must check the outside surface of the guide sleeve for scoring and the duplex bearing for roughness. (Requirement 1, 1.1, 1.2)\n  - Retirement (replacement): The duplex pitch change bearings P/N 47-641-131-1 must be replaced. (Retirement)\n\n- Timing for compliance:\n  - The inspection must be done within 100 hours time in service after 31 August 1970. (Compliance — Para. 1)\n  - The bearing replacement must occur at intervals not exceeding 600 hours total time in service. (Compliance — Para. 2)\n\n- Source reference: The directive also notes a related FAA airworthiness directive (FAA AD 70-14-1). (Note)\n\nWhy the directive exists (as stated or implied by the text):\n- The text requires inspection for scoring and roughness and sets a fixed replacement interval. Those actions imply an intent to find and remove worn or damaged components before they fail. The directive cites the FAA AD as related material. (Requirement; Note)\n\nWho pays and who decides:\n- Aircraft operators or owners pay for the labour and replacement parts when they dismantle the tail rotor drive head, perform the inspections, and replace the bearings. Maintenance personnel or licensed mechanics carry out the dismantling and visual assessments under the directive's instructions. The directive sets the mandatory actions and timing; it leaves the execution (who performs the work and how long it takes) to the operator and their maintenance organisation. (Applicability; Requirement; Compliance)\n\nCosts, incentives and trade-offs (mechanical and economic consequences):\n- Direct costs: labour to dismantle the tail rotor drive head, inspection time, and the recurring cost of replacing the specific bearing P/N 47-641-131-1 at or before 600 hours. (Requirement; Retirement; Compliance)\n- Operational cost: aircraft downtime while the drive head is dismantled and bearings are replaced; scheduling maintenance to meet the 100-hour inspection window (relative to the 31 August 1970 reference point) and the 600-hour replacement interval. (Requirement; Compliance)\n- Supply-side effect: demand for the specified bearing and guide sleeve part numbers may increase for operators of the listed models, which concentrates purchase benefit to manufacturers or suppliers of those parts. (Applicability; Retirement)\n- Implementation risk and discretion: the inspection criteria are descriptive — \"scoring\" on the sleeve and \"roughness\" of the bearing — which introduces some subjectivity into pass/fail judgments by maintenance personnel. That subjectivity can cause variability in when parts are declared unserviceable and replaced. (Requirement 1.1, 1.2)\n- Compliance certainty: the directive prescribes a firm replacement interval (600 hours), which removes discretion on replacement timing but preserves operator discretion on how to schedule and perform the work. (Compliance — Para. 2)\n\nPractical effects on private choices and maintenance practice:\n- Operators must include the inspection and replacement interval in maintenance schedules for affected helicopters. They may choose to replace bearings earlier than the 600‑hour limit if inspections indicate wear. Operators must source the specified part numbers and plan for the labour needed to access and inspect the components. (Applicability; Requirement; Retirement; Compliance)\n\nImplementation notes and potential unintended consequences to monitor:\n- Because the inspection standard uses qualitative descriptors rather than quantitative wear limits, inspection outcomes could vary by inspector and maintenance facility, potentially leading to uneven replacement rates across operators. (Requirement 1.1, 1.2)\n- Fixed replacement intervals reduce the risk of late replacement but impose recurring parts-and-labour costs even when bearings may appear serviceable at the interval. (Retirement; Compliance)\n\nSource citations: Applicability; Requirement (1, 1.1, 1.2); Retirement; Compliance (Para. 1 and Para. 2); Note (FAA AD 70-14-1)."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted airworthiness directive focused on a specific mechanical defect in specific helicopter models. It has not expanded beyond its original safety purpose. The scope remains tightly constrained to the duplex pitch change bearing inspection and replacement requirements as originally intended."},"complexity_factors":["Very short document (approximately 200 words)","Only 4 defined/model variants specified in applicability","Single specific part number targeted (P/N 47-641-131-1)","Clear, sequential numbered requirements (1.1, 1.2, 2)","Simple binary compliance structure (inspection + retirement)","No cross-references to other legislation beyond a single note about FAA AD","No conditional logic or exceptions","Fixed time intervals (100 hours, 600 hours) with no calculations required"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for specific Bell helicopters.\n\n**What it does:**\nThis directive requires owners and operators of certain Bell 47 helicopter models to inspect and eventually replace a specific mechanical part called the \"duplex pitch change bearing\" (part number 47-641-131-1). This bearing is part of the tail rotor system, which is critical for controlling the helicopter's direction.\n\n**Who it affects:**\n- Owners and operators of Bell 47D-1, 47G, 47G-2, and 47H-1 helicopters\n- Specifically those fitted with the duplex pitch change bearing part number 47-641-131-1\n\n**What must be done:**\n1. **Inspection:** Within 100 hours of flying time after 31 August 1970, mechanics must take apart the tail rotor drive head to check:\n   - The guide sleeve for scratches/scoring\n   - The bearing for roughness or damage\n\n2. **Replacement:** The bearing must be replaced entirely every 600 hours of total flight time.\n\n**Why it matters:**\nThis directive was issued because the duplex pitch change bearing was likely found to have a safety defect that could lead to tail rotor failure — a potentially catastrophic event in a helicopter. The 100-hour inspection deadline and 600-hour replacement interval are designed to catch problems before they cause accidents.\n\n**Note:** The reference to \"FAA AD 70-14-1\" indicates this Australian directive aligns with a similar safety order issued by the US Federal Aviation Administration, suggesting this was a known international safety issue."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-47-65-duplex-pitch-change-bearing-inspection-and-retirement","history":"/api/acts/ad-bell-47-65-duplex-pitch-change-bearing-inspection-and-retirement/history","analysis":"/api/acts/ad-bell-47-65-duplex-pitch-change-bearing-inspection-and-retirement/analysis","conflicts":"/api/acts/ad-bell-47-65-duplex-pitch-change-bearing-inspection-and-retirement/conflicts","importantCases":"/api/acts/ad-bell-47-65-duplex-pitch-change-bearing-inspection-and-retirement/important-cases","documents":"/api/acts/ad-bell-47-65-duplex-pitch-change-bearing-inspection-and-retirement/documents"}}