{"id":"F2006B04657","name":"AD/BELL 412/22 - Main Transmission Spiral Bevel Gear","slug":"ad-bell-412-22-main-transmission-spiral-bevel-gear","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44409,"registerId":"commonwealth-F2006B04657-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BELL 412/22 - 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\n![](image.001.png)  \nBell Helicopter Textron 412 Series Helicopters\n\nAD/BELL412/22 Main Transmission Spiral Bevel Gear 7/89\n\nApplicability: All 412 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 Airworthiness Directive maintains its original narrow scope. It addresses a specific safety-critical manufacturing defect in a single part number of Bell 412 helicopter transmissions. The directive has not expanded beyond its original purpose of preventing catastrophic gear failure due to metallurgical inclusions."},"complexity_factors":["Single, specific technical subject matter (one helicopter part)","Clear applicability criteria (specific part number and flight hour threshold)","Two distinct but straightforward inspection requirements","Simple compliance timeline (initial deadline + recurring intervals)","Minimal cross-referencing (only one reference to related FAA directive)","No nested conditional logic or exceptions","Short document length (approximately 250 words)"],"plain_english_summary":"CASA requires immediate inspections on Bell 412 helicopters whose main transmission contains spiral bevel gear P/N 204‑040‑701‑103 with under 250 flight hours. Operators must check the transmission oil filter for metal particles before flight and inspect/remove a cover to examine gear teeth for cracks, chipping or deformation, replacing any damaged parts before flight.\n\nThis targets a manufacturing defect that can cause the gear to fracture in early service, risking loss of main‑rotor drive and catastrophic failure."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The instrument retains a focused scope: it applies only to 412-series helicopters fitted with the listed spiral bevel gear part number that has accumulated less than 250 hours TIS, addressing the early-life failure risk identified by metallurgical examination (Applicability; Background). It does not expand application to other parts, helicopters, or to gears beyond 250 hours."},"complexity_factors":["Narrow technical applicability — limited to Bell 412 helicopters with specific part number P/N 204-040-701-103 and with that gear <250 hours (Applicability).","Multiple, layered compliance timings — initial inspection within 10 hours or 7 days, then recurring inspections at different intervals for filter (daily before first flight) and gear (every 50 hours) until 250 hours (Compliance).","Immediate operational constraint — defects require replacement before further flight, effectively grounding affected aircraft until fixed (Requirement 1 & 2).","Access requirement — inspection requires removal of a quill pad cover or rotor brake quill to view gear teeth, adding labor and downtime (Requirement 2).","Inspection specificity — checks for different evidence types (metal particles in filter; cracks, chipping, deformation of gear teeth), which may require skilled inspection and possible metallurgical assessment (Requirement 1 & 2).","Recordkeeping and monitoring burden — operators must track gear time-in-service up to the 250-hour threshold to cease heightened inspections (Applicability & Compliance).","Cross-reference to FAA Emergency AD — introduces dependence on another regulator's finding for context (Note)."],"plain_english_summary":"This airworthiness directive requires operators of Bell 412 helicopters fitted with spiral bevel gear P/N 204-040-701-103 (with that gear under 250 hours total time‑in‑service) to inspect the transmission sump oil filter and the gear teeth for metal contamination, cracks, chipping or deformation, and to replace any defective parts before further flight. Inspections must be repeated at short, prescribed intervals until the gear reaches 250 hours. It responds to a detected metallurgical inclusion that may cause early gear failure; operators pay inspection, downtime and replacement costs, and the regulator sets timing and grounding rules."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-412-22-main-transmission-spiral-bevel-gear","history":"/api/acts/ad-bell-412-22-main-transmission-spiral-bevel-gear/history","analysis":"/api/acts/ad-bell-412-22-main-transmission-spiral-bevel-gear/analysis","conflicts":"/api/acts/ad-bell-412-22-main-transmission-spiral-bevel-gear/conflicts","importantCases":"/api/acts/ad-bell-412-22-main-transmission-spiral-bevel-gear/important-cases","documents":"/api/acts/ad-bell-412-22-main-transmission-spiral-bevel-gear/documents"}}