{"id":"F2006B07534","name":"AD/UH-1/6 Amdt 2 - Main Rotor Mast and Trunnion","slug":"ad-uh-1-6-amdt-2-main-rotor-mast-and-trunnion","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":50089,"registerId":"commonwealth-F2006B07534-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/UH-1/6 Amdt 2 - Main Rotor Mast and Trunnion","content":"![](image.001.png)\n\n![](image.001.png)  \nAIRWORTHINESS DIRECTIVE\n\nFor the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/UH-1/6 Amdt 1 and issues the following AD under subregulation 39.1 (1) of CAR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.\n\n![](image.001.png)\n\nBell UH-1 Series Helicopters\n\nAD/UH-1/6\n\nAmdt 2\n\n  \n\nMain Rotor Mast and Trunnion 4/2002 DM\n\nApplicability: Models UH-1A, UH-1B, UH-1E, UH-1F, UH-1H, UH-1L, UH-1P, and HH-1K, TH-\n\n1F, TH-1L, and Southwest Florida Aviation SW204, SW204HP, SW205, and SW205A-1 helicopters; equipped with main rotor mast, part number 204-011-450- 007, -105, or -109, or main rotor trunnion, part number 204-011-105-001.\n\nRequirement: Action in accordance with the technical requirements of FAA AD 2002-01-31 Amdt 39-12628.\n\nCompliance: As specified in the Requirement document with a revised effective date of 13 March 2002.\n\nThis Amendment becomes effective on 13 March 2002.\n\nBackground: This Directive was raised following several fatigue failures of the mast and a reported head separation from a 205A-1 helicopter. This Directive requires conversion of flight hours to Retirement Index Numbers and an inspection of each main rotor mast for burr or an inadequate radius in the snap ring groove.\n\nAmendment 1 was prompted by the discovery of a crack in a main rotor mast with a lower Retirement Index Number value than the established life limit. Certain actions were necessary to preclude the occurrence of a fatigue crack in the damper splined area of a main rotor mast.\n\nAmendment 2 is issued in response to a new FAA AD which establishes a retirement life for the main rotor trunnion based on monitoring the number of torque events and flight hours rather than flight hours only as currently required; and also adds a note clarifying that the mast serial number is defined by 5 or fewer digits plus various prefixes.\n\nBell UH-1 Series Helicopters\n\nAD/UH-1/6 Amdt 2 (continued)\n\nThe original issue of this Airworthiness Directive became effective on 28 April 2000.\n\nAmendment 1 of this Airworthiness Directive became effective on 15 November 2000.\n\n![Signature of David Alan Villiers Delegate of the Civil Aviation Safety Authority](image.002.png)  \n\nDavid Alan Villiers\n\nDelegate of the Civil Aviation Safety Authority 6 March 2002\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 13 March 2002.","sortOrder":0}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"The legislation maintains its original scope as a safety-critical airworthiness directive targeting specific mechanical failures in the UH-1 helicopter fleet. Amendment 2 represents a technical refinement within the established safety framework rather than scope expansion — it updates the methodology for determining component retirement (adding torque events to flight hours) and clarifies serial number identification, but does not extend applicability to new aircraft types or introduce unrelated regulatory requirements."},"complexity_factors":["Heavy reliance on external document: The core technical requirements are not contained in the directive itself but reference FAA AD 2002-01-31 Amdt 39-12628, requiring operators to obtain and cross-reference a separate US regulatory document","Technical aviation terminology: Uses specialized terms like 'Retirement Index Numbers', 'torque events', 'trunnion', 'snap ring groove', and 'damper splined area' without in-text definitions","Multiple predecessor versions: References Amendment 1 and original issue (2000), requiring historical awareness to understand the evolution of requirements","Conditional applicability: Applies only to specific part numbers (204-011-450-007, -105, -109 for masts; 204-011-105-001 for trunnions) across multiple helicopter models","Dual compliance metrics: Introduces a two-factor retirement calculation (torque events + flight hours) replacing a single-factor system, adding record-keeping burden"],"plain_english_summary":"This AD revokes and replaces a prior safety order, mandating that owners/operators of Bell UH-1 series helicopters with specified main rotor mast or trunnion parts follow FAA technical instructions to prevent catastrophic rotor mast/trunnion failures.  \n\nIt’s safety-critical—addressing fatigue cracks that have caused rotor separations—and introduces new retirement limits based on both torque events and flight hours (not hours alone). Compliance is required from 13 March 2002."},"flash_summary":{"complexity_score":6,"scope_assessment":{"changed":true,"description":"Amendment 2 modifies scope by adopting a new FAA AD approach that establishes trunnion retirement based on both torque-event counts and flight hours (instead of flight hours alone) and by adding a note clarifying mast serial-number format; it retains the prior requirements to convert hours to Retirement Index Numbers and to inspect masts for burrs or inadequate snap‑ring groove radii, and it replaces the earlier AD (effective 13 March 2002)."},"complexity_factors":["Cross-reference to an external FAA AD (FAA AD 2002-01-31) for technical requirements, creating dependency on another instrument for compliance details","Multiple affected airframes and specific part numbers across Bell UH-1 models and several Southwest Florida variants","Change from a single metric (flight hours) to a compound retirement metric (flight hours plus number of torque events) for trunnions","Requirement to convert flight hours into Retirement Index Numbers (RINs), which imposes record-keeping and calculation tasks on operators","Technical inspection criteria (burrs, inadequate radius in snap ring groove) require detailed maintenance checks and possible tooling/expertise","Amendment history (revocation of prior AD and revised effective dates) increases procedural tracking burdens for operators and regulators","Clarification of mast serial-number formats (prefixes and up to five digits) adds administrative interpretation tasks for identifying affected parts"],"plain_english_summary":"This directive updates mandatory inspection and retirement rules for specified Bell UH‑1 and certain Southwest Florida helicopters by adopting the technical requirements of FAA AD 2002‑01‑31, effective 13 March 2002. It requires operators to convert flight hours to Retirement Index Numbers, inspect main rotor masts for burrs or inadequate snap‑ring groove radii, and to monitor torque events as well as flight hours when retiring main rotor trunnions. Aircraft owners/operators must carry out and pay for the required inspections and part retirements; CASA enforces compliance."}},"importantCases":[],"_links":{"self":"/api/acts/ad-uh-1-6-amdt-2-main-rotor-mast-and-trunnion","history":"/api/acts/ad-uh-1-6-amdt-2-main-rotor-mast-and-trunnion/history","analysis":"/api/acts/ad-uh-1-6-amdt-2-main-rotor-mast-and-trunnion/analysis","conflicts":"/api/acts/ad-uh-1-6-amdt-2-main-rotor-mast-and-trunnion/conflicts","importantCases":"/api/acts/ad-uh-1-6-amdt-2-main-rotor-mast-and-trunnion/important-cases","documents":"/api/acts/ad-uh-1-6-amdt-2-main-rotor-mast-and-trunnion/documents"}}