{"id":"F2006L00723","name":"AD/BELL 427/2 - Horizontal Stabiliser Auxiliary Fin Assemblies","slug":"ad-bell-427-2-horizontal-stabiliser-auxiliary-fin-assemblies","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":136748,"registerId":"commonwealth-F2006L00723-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Bell Helicopter Textron 427 Series Helic","sectionType":"division","heading":"Bell Helicopter Textron 427 Series Helicopters","content":"### Bell Helicopter Textron 427 Series Helicopters\n\n| AD/BELL 427/2 | Horizontal Stabiliser Auxiliary Fin Assemblies | 4/2006 |\n| ------------- | ---------------------------------------------- | ------ |\n\n| Applicability: | Model 427 helicopters, serial numbers 56001 through 56030 with auxiliary fin assemblies, part numbers 427-035-836-101, -102, -105, or -106, installed.                                                                                                                                                                                                                                                                                                                                                                                                                         |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n| Requirement:   | Modify auxiliary fin assemblies, part numbers 427-035-836-101, -102, -105, or -106, in accordance with the Accomplishment Instructions in Bell Helicopter Textron (BHT) Alert Service Bulletin 427-01-07, dated 16 November 2001.After accomplishing the modification, reduce the never-exceed-speed (Vne) limitation for a pedal stop failure from 80 knots indicated airspeed (KIAS) to 60 KIAS; by incorporating BHT Rotorcraft Flight Manual BHT-427-FM-2 Revision 5, dated 23 April 2002.Note: FAA AD 2003-04-12 Amdt 39-13061 and Transport Canada ADCF-2001-05R1 refer. |\n| Compliance:    | Within 60 days after 13 April 2006, unless already accomplished.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |\n|                | This Airworthiness Directive becomes effective on 13 April 2006.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |\n| Background:    | Reports were received of several incidents of main rotor blades contacting the top of the auxiliary fins, resulting in an upper tuning weight coming loose. This Directive requires modification of the overall height of the auxiliary fins to prevent main rotor blade contact, loss of a tuning weight with possible impact with a tail or main rotor blade, and subsequent loss of control of the helicopter.                                                                                                                                                              |\n\n![](image.001.png)  \nDavid Punshon  \nDelegate of the Civil Aviation Safety Authority\n\n1 March 2006","sortOrder":0},{"sectionNumber":"AD/BELL 427/2","sectionType":"part","heading":"AD/BELL 427/2","content":"## AD/BELL 427/2","sortOrder":1},{"sectionNumber":"Horizontal Stabiliser Auxiliary Fin Asse","sectionType":"part","heading":"Horizontal Stabiliser Auxiliary Fin Assemblies","content":"## Horizontal Stabiliser Auxiliary Fin Assemblies","sortOrder":2},{"sectionNumber":"4/2006","sectionType":"part","heading":"4/2006","content":"## 4/2006","sortOrder":3}],"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":2,"scope_assessment":{"changed":false,"description":"This AD maintains its original narrow scope — addressing a specific mechanical defect in a limited fleet of helicopters. There is no evidence of scope creep; it targets exactly the safety issue identified (rotor blade contact with auxiliary fins) without expanding into broader operational or design requirements."},"complexity_factors":["Single, specific applicability: only 30 helicopter serial numbers with 4 specific part numbers","Straightforward two-part requirement: (1) physical modification per manufacturer bulletin, (2) manual update with speed limit reduction","Single compliance deadline with simple exception ('unless already accomplished')","Minimal cross-referencing: only refers to manufacturer documents (BHT Alert Service Bulletin and Flight Manual Revision) and notes related foreign ADs without incorporating them","No nested conditions, exceptions, or defined terms section","Clear causal background explaining the safety risk in plain language","Total length: approximately 250 words of substantive content"],"plain_english_summary":"CASA issued a mandatory AD requiring owners/operators of Bell 427 helicopters (S/N 56001–56030) to modify auxiliary tail fin assemblies to increase fin height and prevent main rotor strikes. Maintenance must perform the change; compliance was required within 60 days of 13 April 2006.\n\nThe AD also reduces the allowed airspeed in a pedal-stop failure from 80 KIAS to 60 KIAS. It responds to incidents where rotor-to-fin contact released a tuning weight and risked loss of control."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The Directive does not expand applicability beyond the specified helicopters and part numbers. It implements a corrective modification and an operational speed limit consistent with the stated safety objective, rather than introducing new categories of obligation or beneficiaries."},"complexity_factors":["Narrow applicability: specific serial number range and four part numbers (raises administrative precision but simplifies targeting).","Technical modification mandated by manufacturer service bulletin (requires access to and execution of detailed maintenance instructions).","Operational change: mandatory Vne reduction for a defined failure condition (requires flight manual amendment and operational discipline).","Short compliance window (60 days) increases logistical pressure on operators and maintenance providers.","Safety-critical consequence if not complied with (loss of control risk), creating strict regulatory enforcement and record-keeping requirements.","Cross-references to FAA and Transport Canada advisories (coordination of international compliance expectations)."],"plain_english_summary":"This Airworthiness Directive requires owners/operators of Bell 427 helicopters (serials 56001–56030) fitted with specific auxiliary fin assemblies (P/Ns 427-035-836-101, -102, -105, -106) to modify those fins per Bell Alert Service Bulletin 427-01-07 and to reduce the Vne for a pedal-stop failure from 80 KIAS to 60 KIAS. Compliance is required within 60 days of 13 April 2006. The rule is intended to prevent main rotor blade contact and loss of a tuning weight; operators must schedule the modification, update flight manuals and absorb the maintenance costs."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-427-2-horizontal-stabiliser-auxiliary-fin-assemblies","history":"/api/acts/ad-bell-427-2-horizontal-stabiliser-auxiliary-fin-assemblies/history","analysis":"/api/acts/ad-bell-427-2-horizontal-stabiliser-auxiliary-fin-assemblies/analysis","conflicts":"/api/acts/ad-bell-427-2-horizontal-stabiliser-auxiliary-fin-assemblies/conflicts","importantCases":"/api/acts/ad-bell-427-2-horizontal-stabiliser-auxiliary-fin-assemblies/important-cases","documents":"/api/acts/ad-bell-427-2-horizontal-stabiliser-auxiliary-fin-assemblies/documents"}}