{"id":"F2006B04449","name":"AD/BELL 206/135 - Main Rotor Trunnion and Mast","slug":"ad-bell-206-135-main-rotor-trunnion-and-mast","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44286,"registerId":"commonwealth-F2006B04449-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BELL 206/135 - Main Rotor Trunnion and Mast","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 Canada (BHTC) 206 and Agusta Bell 206 Series Helicopters\n\nAD/BELL 206/135 Main Rotor Trunnion and Mast 10/95\n\nApplicability: All Bell 206L, 206L-1, 206L-3 and 206L-4 helicopters fitted with main rotor trunnion P/N 206-011-120-103 and mast P/N 206-040-535-001/-005/-101 /-105.\n\nNote: Main rotor trunnion P/N 206-011-120-001 is no longer permitted to remain in service.\n\nRequirement: Retire the main rotor trunnion before it has attained a Retirement Index Number (RIN) of 24 000 as adjusted in Bell ASB 206L-94-99, Revision A, Table 3.\n\nRetire the mast before it has attained a RIN of 44 000 as adjusted in Table 4, or before the time in service as adjusted in Table 2 of Bell ASB 206L-94-99, Revision A, whichever occurs first.\n\nCompliance: Before 100 hours time in service after 14 September 1995 but no later than 17 December 1995.\n\nBackground: Bell Helicopter’s fatigue testing and analysis have shown that the life of certain critical components can be estimated in a more accurate manner when the calculations are based on changes in power. The fatigue life is no longer to be based on component hours but on the number of power change events. A history card for each component will have to be created to document the Retirement Index Number.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific fatigue issue in specific helicopter models. It has not expanded beyond its original purpose of mandating retirement of critical rotating components."},"complexity_factors":["Multiple part number variations requiring cross-checking (4 mast part numbers, 2 trunnion part numbers)","Dual retirement criteria for the mast (RIN of 44,000 OR time in service, whichever comes first)","Single retirement criterion for trunnion (RIN of 24,000)","Reference to external technical document (Bell ASB 206L-94-99, Revision A) with specific tables (Tables 2, 3, and 4) not reproduced in the directive","Requires creation of new documentation systems (history cards for RIN tracking)","Conditional applicability based on installed parts","Complex compliance window (dual deadline: hours-based AND calendar-based)"],"plain_english_summary":"This CASA Airworthiness Directive requires owners/operators of certain Bell 206L-series helicopters to permanently remove and replace the main rotor trunnion and mast before they reach a calculated fatigue limit. It replaces simple flight-hour limits with Retirement Index Numbers (RIN) based on power changes, and mandates tracking history cards. The rule affects operators and maintenance organisations and prevents catastrophic rotor failures from fatigue cracks. Compliance deadlines were set in 1995."},"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"The directive changes the retirement criterion from component hours to a Retirement Index Number (RIN) based on power-change events and sets specific RIN thresholds and alternative time‑in‑service limits for trunnions and masts. It also expressly prohibits continued use of main rotor trunnion P/N 206-011-120-001 and mandates creation of component history cards to record RIN accumulation. These changes alter how operators measure life limits, increase record-keeping duties, and impose mandatory retirements by specified dates."},"complexity_factors":["Reliance on external service document: retirement limits and adjustment tables are set by Bell ASB 206L-94-99 Revision A rather than fully within the AD.","New life metric: shifts from component hours to Retirement Index Number (RIN) measured by power-change events, requiring operators to translate operational activity into RINs.","Specific numeric thresholds: RIN = 24,000 for trunnion and RIN = 44,000 for mast plus alternative time‑in‑service limits.","Record-keeping burden: mandatory creation and maintenance of a history card for each affected component to document RIN accrual.","Multiple affected parts and airframe variants: several part numbers and Bell 206L/206L-1/206L-3/206L-4 models are covered, increasing tracking complexity for mixed fleets.","Short compliance window: specified mandatory compliance dates create a time-sensitive replacement schedule for operators.","Absolute prohibition: one trunnion part number (P/N 206-011-120-001) is explicitly no longer permitted in service, requiring immediate fleet inventory checks."],"plain_english_summary":"This airworthiness directive requires operators of specified Bell 206L-series helicopters to retire certain main rotor trunnions and masts at set Retirement Index Numbers (RINs) or by specified service times, and bans trunnion P/N 206-011-120-001 from further use. It replaces hour-based life limits with a power-change‑event (RIN) basis and requires a history card for each component to record RINs. Operators must track RINs per Bell ASB 206L-94-99 Revision A and remove parts by the stated deadlines; CASA enforces compliance."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-206-135-main-rotor-trunnion-and-mast","history":"/api/acts/ad-bell-206-135-main-rotor-trunnion-and-mast/history","analysis":"/api/acts/ad-bell-206-135-main-rotor-trunnion-and-mast/analysis","conflicts":"/api/acts/ad-bell-206-135-main-rotor-trunnion-and-mast/conflicts","importantCases":"/api/acts/ad-bell-206-135-main-rotor-trunnion-and-mast/important-cases","documents":"/api/acts/ad-bell-206-135-main-rotor-trunnion-and-mast/documents"}}