{"id":"F2006B04673","name":"AD/BELL 412/39 Amdt 1 - Tail Rotor Yoke and Tail Rotor Flapping Stop/Indicator","slug":"ad-bell-412-39-amdt-1-tail-rotor-yoke-and-tail-rotor-flapping-stop-indicator","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44425,"registerId":"commonwealth-F2006B04673-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BELL 412/39 Amdt 1 - Tail Rotor Yoke and Tail Rotor Flapping Stop/Indicator","content":"![](image.001.png)  \n![](image.002.png)  \nBell Helicopter Textron 412 Series Helicopters\n\nAIRWORTHINESS DIRECTIVE\n\n![](image.002.png)\n\n![](image.002.png)  \nFor the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/BELL 412/39 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\nAD/BELL 412/39\n\nAmdt 1\n\n  \n\nTail Rotor Yoke and Tail Rotor Flapping Stop/Indicator\n\n  \n8/2001\n\nApplicability: All Model 412, 412CF, and 412EP helicopters, with tail rotor yoke assembly, part number 212-011-702-all dash numbers, installed.\n\nRequirement: 1. Review the historical records of the yoke assembly, for any static or dynamic overload damage that could have imposed a bending load on the yoke. The damage may not have required replacing the yoke assembly; for example, an incident in which a damaged tail rotor blade was replaced due to a blade strike. If the records indicate that overload damage may have occurred, replace the yoke with a serviceable yoke.\n\n    2. (a) Install a Never Exceed Velocity (Vne) red line at 120 knots indicated airspeed (KIAS) on the pilot and copilot airspeed indicators using red tape or paint, and a slippage indicator on the instrument case and glass.\n\n    (b) Install a placard made of material that is not easily erased, or disfigured, or obscured on the instrument panel in clear view of the pilot and copilot:\n\n“Observe temporary Maximum Never Exceed (Vne) airspeed red line (marked at 120 knots indicated airspeed (KIAS). Vne is 20 KIAS less than the value presented on the airspeed limitation placard for each ambient condition”.\n\n    (c) A Rotorcraft Flight Manual Temporary Revision, dated 16 August 1996 is required.\n\n    3. (a) Remove rotor yoke assembly, part number 212-011-702-all dash numbers, and replace it with a serviceable yoke assembly, part number 212-011-702-all dash numbers, with zero hours time in service, or an airworthy yoke that has passed a one-time x-ray diffraction inspection in accordance with Bell Helicopter Textron Alert Service Bulletin (ASB) 412-96-89 Revision A, dated 17 October 1997, or ASB 412CF-96-01, dated 3 September 1996, as applicable.\n\n    (b) Install a serviceable tail rotor flapping stop, part number 212-011-713-103.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n    (c) If requirements 3(a) and 3(b) are accomplished in accordance with this Directive, remove the 120 KIAS redline from the pilot and copilot airspeed indicators; remove the Vne airspeed restriction placard; and remove the Bell Helicopter Textron Temporary Revision, dated 16 August 1996, from the Rotorcraft Flight Manual.\n\n    4. Inspect the yoke assembly and tail rotor flapping stop in accordance with Part III, Recurring 25-Hour Special Inspection and Conditional Inspection Requirement, of Bell Helicopter Textron ASB 412-96-89, Revision A, dated 17 October 1996, or ASB 412CF-96-01, dated 3 September 1996, as applicable.\n\nNote: FAA AD 2001-09-11 Amdt 39-12217 refers.\n\nCompliance: 1. Unless already accomplished, before further flight after 29 April 1998.\n\n    2. Unless Requirement 3 is already accomplished, before further flight after 29 April 1998.\n\n    3. Unless already accomplished, before 30 Oct 1998.\n\n    4. After accomplishment of Requirement 3; at intervals not to exceed 25 hours time in service.\n\nThe compliance times of the original issue of this Directive remain unchanged by this issue.\n\nThis amendment becomes effective on 9 August 2001.\n\nBackground: The actions required by the FAA are prompted by laboratory tests and engineering analysis that indicated that the yoke assembly is susceptible to fatigue damage due to unforeseen static and dynamic loading of the tail rotor against the original flapping stop. Failure of the yoke could result in loss of the tail rotor and subsequent loss of control of the helicopter.\n\nAmendment 1 is issued in response to a new FAA AD which expands applicability to all Model 412 helicopters. This action was prompted by the determination that the unsafe condition exists on all Model 412 helicopters, regardless of serial number.\n\n![](image.003.png)The original issue of this Airworthiness Directive became effective on 29 April 1998.\n\n![](image.004.png)  \n\nDavid Alan Villiers\n\nDelegate of the Civil Aviation Safety Authority 3 July 2001\n\n![](image.002.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 11 July 2001.","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"},"flash_summary":{"complexity_score":6,"scope_assessment":{"changed":true,"description":"Amendment 1 expands applicability to all Model 412 helicopters regardless of serial number. The original AD (effective 29 April 1998) is retained in its compliance timing, but this amendment broadened which aircraft are captured by the directive."},"complexity_factors":["Multiple distinct mandatory actions: records review, temporary placards/Flight Manual revision, one‑time replacement/inspection, recurring inspections.","Technical inspection requirement: one‑time x‑ray diffraction inspection or replacement with zero‑hour part (specialist equipment/skills).","Specific part numbers mandated (yoke and flapping stop) creating parts-procurement burden and potential lead times.","Staggered, time‑critical compliance deadlines (before further flight dates and a later hard replacement date).","Recurring 25‑hour inspection interval increases maintenance frequency and operating cost.","Cross-references to Bell Alert Service Bulletins and FAA AD for inspection methods and applicability.","Potential grounding or operational restrictions until compliance (temporary Vne and placards; before‑flight requirements).","Record-keeping and judgment required to determine whether past events constituted overload damage."],"plain_english_summary":"Requires operators of Bell 412, 412CF and 412EP helicopters with tail rotor yoke P/N 212-011-702 to review records for possible overload damage, install temporary 120 KIAS Vne markings and a Flight Manual temporary revision, replace or x‑ray inspect the yoke, fit a specified tail rotor flapping stop, and carry out recurring 25‑hour inspections. The AD responds to a fatigue risk in the tail rotor yoke that could lead to loss of the tail rotor; it imposes parts, inspection and potential downtime costs on operators."},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":true,"description":"The original AD (effective 29 April 1998) applied to a limited range of serial numbers. Amendment 1 (effective 9 August 2001) expands applicability to 'all Model 412 helicopters, regardless of serial number' after the FAA determined the unsafe condition was more widespread than initially assessed. This significantly broadens the regulatory burden from a targeted subset to the entire fleet type."},"complexity_factors":["Multiple interdependent requirements (Requirements 1-4) with cross-references between them (e.g., Requirement 2's temporary measures only apply 'unless Requirement 3 is already accomplished')","Specific part numbers and document references (Bell ASB 412-96-89 Revision A, ASB 412CF-96-01, FAA AD 2001-09-11) that operators must locate and follow","Conditional compliance logic with multiple deadlines and exceptions ('unless already accomplished', 'before further flight', 'before 30 Oct 1998')","Technical aviation terminology requiring specialised knowledge (Vne, KIAS, time in service, Alert Service Bulletin, dash numbers)","Nested conditions in Requirement 3(c) requiring removal of temporary measures only if 3(a) and 3(b) are completed"],"plain_english_summary":"This CASA Airworthiness Directive requires owners/operators of Bell 412/412CF/412EP helicopters with tail rotor yoke P/N 212‑011‑702 to take urgent action to prevent tail rotor yoke fatigue and in‑flight separation. It mandates record reviews for past hard landings, temporary speed/placard/flight‑manual limits, and a permanent yoke replacement or X‑ray‑inspected serviceable yoke plus an improved flapping stop, followed by recurring inspections. The amendment expands applicability to all Model 412s to prevent catastrophic loss of control."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-412-39-amdt-1-tail-rotor-yoke-and-tail-rotor-flapping-stop-indicator","history":"/api/acts/ad-bell-412-39-amdt-1-tail-rotor-yoke-and-tail-rotor-flapping-stop-indicator/history","analysis":"/api/acts/ad-bell-412-39-amdt-1-tail-rotor-yoke-and-tail-rotor-flapping-stop-indicator/analysis","conflicts":"/api/acts/ad-bell-412-39-amdt-1-tail-rotor-yoke-and-tail-rotor-flapping-stop-indicator/conflicts","importantCases":"/api/acts/ad-bell-412-39-amdt-1-tail-rotor-yoke-and-tail-rotor-flapping-stop-indicator/important-cases","documents":"/api/acts/ad-bell-412-39-amdt-1-tail-rotor-yoke-and-tail-rotor-flapping-stop-indicator/documents"}}