{"id":"F2006B04390","name":"AD/BELL 205/54 - Main Transmission Spiral Bevel Gear","slug":"ad-bell-205-54-main-transmission-spiral-bevel-gear","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44215,"registerId":"commonwealth-F2006B04390-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BELL 205/54 - Main Transmission Spiral Bevel Gear","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\nBell Helicopter Textron 205 Series Helicopters\n\nAD/BELL 205/54 Main Transmission Spiral Bevel Gear 7/89\n\nApplicability: All 205A and 205A-1 series helicopters with main transmission containing spiral bevel gear P/N 204-040- 701-103 with less than 250 hours total time in service.\n\nRequirement: 1. Remove and inspect the transmission internal sump oil filter for evidence of metal contamination (eg, steel particles in splinter, granular or flake form). If metal contamination is evident replace worn parts before further flight. Refit oil filter.\n\n2. Remove a quill pad cover P/N 204-040-174-001 or rotor brake quill from the transmission main ring gear case to allow access to the spiral bevel gear. Inspect all teeth of the gear for evidence of cracks, chipping and deformation. If cracks, chipping or metal deformation is evident replace gear before further flight. Refit component removed for access.\n\nNote: FAA Emergency AD 89-08-05 refers.\n\nCompliance: 1. Within 10 hours time in service or seven days whichever occurs first after 8 May 1989. Thereafter reinspect before the first flight of the day until gear has operated for 250 hours time in service.\n\n2. Within 10 hours time in service or seven days whichever occurs first after 8 May 1989. Thereafter reinspect at intervals not exceeding 50 hours time in service until gear has operated for 250 hours time in service.\n\nBackground: After a pilot reported an occasional unusual noise in flight, inspection of the main transmission revealed two large pieces of gear teeth that had fractured from the spiral bevel gear P/N 204-040-701-103. Metallurgical examination revealed the presence of a low alloy metallic inclusion which occurred during processing of the gear material. This inclusion may result in failure of the gear within the first 250 hours time in service.","sortOrder":0}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific manufacturing defect in a specific helicopter component. It has not expanded beyond its original purpose of preventing gear failure in early-life transmissions."},"complexity_factors":["Single specific technical subject matter (one gear part number)","Two distinct compliance requirements with different ongoing intervals","Specific part numbers referenced (P/N 204-040-701-103, P/N 204-040-174-001)","Conditional logic: 'if contamination evident' and 'if cracks evident' trigger mandatory replacement","Time-based compliance with dual triggers (hours OR days)","Cross-reference to US FAA Emergency AD 89-08-05","Limited applicability criteria (specific helicopter models, specific gear, hour threshold)"],"plain_english_summary":"This Airworthiness Directive affects owners/operators of Bell 205A/205A‑1 helicopters fitted with spiral bevel gear P/N 204‑040‑701‑103 and mandates immediate and repeated inspections of the main transmission (oil filter and gear teeth) while that gear has under 250 flight hours. \n\nIt responds to a reported noise and a manufacturing defect that can shed gear teeth early in service, risking catastrophic transmission failure and loss of the helicopter."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"This AD remains within the original, stated purpose: to detect and prevent early failure of a specific spiral bevel gear (P/N 204-040-701-103) caused by a manufacturing inclusion that may lead to failure within the first 250 hours TIS. It does not expand regulation beyond that safety-focused scope (inspections and replacement when contamination/damage is found) and imposes time-limited measures tied to the 250-hour exposure window."},"complexity_factors":["Short, self-contained document (one AD covering a narrow issue)","Clear applicability criteria (specific airframe models + specific parts P/N + <250 hours TIS)","Two discrete requirements (oil filter inspection and gear tooth inspection)","Two compliance timing regimes: initial within 10 hours or 7 days, then recurring inspections (daily for filter; every 50 hours for gear)","Simple conditional replacement rule (replace if contamination/damage found)","Requirement to remove specific access components (quill pad cover or rotor brake quill) adds a minor procedural step","Cross-reference to FAA Emergency AD (external normative reference)","No extensive defined terms or multi-part exceptions"],"plain_english_summary":"**What this instrument does (mechanically)**\n\n- It orders specific inspections and actions for Bell Helicopter Textron 205 series helicopters that have a particular main transmission spiral bevel gear (part number 204-040-701-103) and that gear has accumulated less than 250 hours total time-in-service (TIS).\n- Two inspection actions are required:\n  - Requirement 1: Remove and inspect the transmission internal sump oil filter for metal contamination (steel particles). If contamination is found, worn parts must be replaced before the helicopter is flown again, and the filter is refitted.\n  - Requirement 2: Remove a quill pad cover (P/N 204-040-174-001) or rotor brake quill to access the spiral bevel gear, inspect every tooth for cracks, chipping or deformation, and replace the gear before further flight if any such damage is found. Refit the removed access component after inspection.\n- Timing and repeat inspections:\n  - Both inspections must be done within 10 hours time-in-service or seven days (whichever happens first) after 8 May 1989.\n  - After that initial inspection:\n    - The oil filter inspection (Requirement 1) must be done before the first flight of each day until the gear has accumulated 250 hours TIS.\n    - The gear tooth inspection (Requirement 2) must be repeated at intervals not exceeding 50 hours TIS until the gear reaches 250 hours TIS.\n- The AD notes an FAA Emergency AD (89-08-05) as related material and explains why the action is required (see below).\n\n**Who it affects**\n\n- Owners and operators of Bell 205A and 205A-1 helicopters that have the specified main transmission spiral bevel gear (P/N 204-040-701-103) and where that gear has less than 250 hours on it.\n- Maintenance organisations and technicians who perform inspections and repairs on these helicopters.\n- Potentially, parts suppliers for replacement gears, filters and access components.\n\n**Why it matters (stated rationale and practical effect)**\n\n- Stated rationale: A pilot reported an unusual noise. Inspection found two large fractured gear-tooth pieces. Metallurgical analysis showed a low-alloy metallic inclusion in the gear material that can cause early failure of the gear within the first 250 hours TIS. The AD’s stated purpose is to detect contamination or early damage so that a failing gear is removed before it can cause a catastrophic transmission failure.\n- Practical effect: The AD increases short-term inspection and potential replacement activity for affected helicopters while the high-risk early service window (first 250 hours) is in effect. It aims to detect either metal contamination (via the filter) or direct gear damage (visual tooth inspection) before further flight, reducing the risk that a detached tooth or fractured gear causes a major transmission failure.\n\n**Costs, incentives and trade-offs**\n\n- Who pays: Operators pay the direct costs — labour for additional inspections, downtime while inspections or replacements occur, and the cost of replacement parts if contamination or damage is found.\n- Incentives: The AD creates an incentive for operators to check part numbers and TIS carefully and to perform frequent inspections or to replace the gear early to avoid repeated inspection burden. Maintenance providers receive more billable inspections and possible repair work.\n- Opportunity cost and productivity: Increased inspection frequency (daily oil-filter checks and 50-hour gear inspections) can reduce aircraft availability and increase operational costs during the affected time window, which may affect scheduling and revenue for operators.\n- Implementation risk and compliance burden: Access to the gear requires removing a quill pad cover or rotor brake quill—tasks that require a maintenance environment and time. Small operators without in-house maintenance capability may need to arrange shop visits, causing logistical and cost burdens. There is limited bureaucratic discretion; the AD prescribes specific inspections and thresholds.\n- Effects on private enterprise and markets: The AD creates short-term demand for replacement gears, filters and maintenance services. It does not change ownership rights or broader market competition, but it can increase operating costs for affected operators.\n- Concentrated benefits and diffuse costs: The safety benefit (avoiding in-flight transmission failure) is concentrated for the specific fleet of helicopters that have the susceptible part; costs are concentrated on those operators but spread across flights during the 250-hour exposure window. There is no obvious mechanism in the AD that creates a recurring regulatory market advantage for particular suppliers beyond normal demand for replacement parts.\n- Substitution effects and unintended consequences: Operators may choose to replace the gear pre-emptively rather than endure repeated inspections, or restrict aircraft use until the 250-hour exposure passes. Those actions increase upfront cost but reduce inspection burden. The AD does not mandate replacement in the absence of contamination or damage, so pre-emptive replacement is a commercial choice.\n\n**Procedural note**\n\n- The AD’s actions are time-bound relative to the gear’s service hours (the 250-hour window). After a gear has passed 250 hours TIS, this AD’s repeated inspections no longer apply to that gear according to the compliance language.\n\n**Reference to related regulation**\n\n- The AD expressly notes the FAA Emergency AD 89-08-05 as relevant background; the Commonwealth AD follows with equivalent mandatory measures for Australian operators.\n\n(References in the AD: “Requirement 1” and “Requirement 2”; the Compliance timings; Background describing metallurgical inclusion.)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-205-54-main-transmission-spiral-bevel-gear","history":"/api/acts/ad-bell-205-54-main-transmission-spiral-bevel-gear/history","analysis":"/api/acts/ad-bell-205-54-main-transmission-spiral-bevel-gear/analysis","conflicts":"/api/acts/ad-bell-205-54-main-transmission-spiral-bevel-gear/conflicts","importantCases":"/api/acts/ad-bell-205-54-main-transmission-spiral-bevel-gear/important-cases","documents":"/api/acts/ad-bell-205-54-main-transmission-spiral-bevel-gear/documents"}}