{"id":"F2007L04214","name":"AD/BELL 427/6 - Disc Assemblies - Tail Rotor Driveshaft","slug":"ad-bell-427-6-disc-assemblies-tail-rotor-driveshaft","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":70408,"registerId":"commonwealth-F2007L04214-current","compilationNumber":null,"startDate":"2026-04-02","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 427/6 | Disc Assemblies - Tail Rotor Driveshaft | 12/2007 |\n| ------------- | --------------------------------------- | ------- |\n\n| Applicability: | Bell Helicopter Textron Canada (BHTC) Model 427 helicopters S/N up to 56056and 58001 through 58002, fitted with disc assemblies part number (P/N)407-340-340-103.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |\n| -------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | 1. Verify disc assemblies P/N 407-340-340-103 for manufacturing date, proper thickness and indexing, in accordance with the instructions provided in BHTC Alert Service Bulletin (ASB) ASB-427-07-17 dated 28 March 2007 or later approved revisions.If disc assemblies, after verification in accordance with Requirement 1, do not require any further action, or if the manufacturing date is not between 1 November 2005 and 30 November 2006, make an appropriate log book entry to this effect. No further action is required.2. Remove any disc assembly which is not within the required thickness of 0.115 - 0.127 inch (2.921 - 3.225 mm).3. Remove any disc assembly which is not properly indexed.4. Do not install any disc assembly P/N 407-340-340-103 into any helicopter unless it is compliant to the ASB-427-07-17 dated 28 March 2007 or later approved revisions.Note: Transport Canada Airworthiness Directive CF-2007-14 dated 24 August 2007 refers. |\n| Compliance:    | 1. Unless already accomplished, no later than 25 flight hours or 30 days from the effective date of this directive, whichever comes first.2. Within 10 flight hours, after the completion of requirement 1.3. Within 300 flight hours or at next scheduled inspection, whichever comes first, after the completion of requirement 1.4. After the effective date of this Airworthiness Directive.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |\n|                | This Airworthiness Directive becomes effective on 22 November 2007.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |\n\n| Background: | Transport Canada has determined that disc assemblies part number (P/N)407-340-340-103 manufactured between 1 November 2005 and 30 November 2006, may have discs of improper thickness or discs may have been indexed incorrectly. |\n| ----------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n\n![](image.001.png)  \nDavid Villiers  \nDelegate of the Civil Aviation Safety Authority\n\n28 September 2007","sortOrder":0},{"sectionNumber":"AD/BELL 427/6","sectionType":"part","heading":"AD/BELL 427/6","content":"## AD/BELL 427/6","sortOrder":1},{"sectionNumber":"Disc Assemblies - Tail Rotor Driveshaft","sectionType":"part","heading":"Disc Assemblies - Tail Rotor Driveshaft","content":"## Disc Assemblies - Tail Rotor Driveshaft","sortOrder":2},{"sectionNumber":"12/2007","sectionType":"part","heading":"12/2007","content":"## 12/2007","sortOrder":3}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a standard, targeted airworthiness directive addressing a specific manufacturing defect in a specific aircraft part. The scope remains precisely limited to the identified safety issue with Bell 427 tail rotor driveshaft disc assemblies. There is no evidence of scope creep; the directive maintains its original purpose of addressing the improper thickness and indexing defects identified by Transport Canada."},"complexity_factors":["Single, specific mechanical component targeted (disc assembly P/N 407-340-340-103)","Clear conditional logic: manufacturing date window (1 Nov 2005 – 30 Nov 2006) determines action","Four distinct requirements with specific, measurable compliance thresholds (thickness 0.115–0.127 inch, indexing status)","Multiple compliance timeframes tied to flight hours and calendar days, creating a cascading schedule","Cross-reference to Canadian authority (Transport Canada AD CF-2007-14) and manufacturer service bulletin (ASB-427-07-17)","Limited applicability: specific helicopter model and serial number range only","No nested exceptions or complex definitional sections — requirements are procedural and mechanical"],"plain_english_summary":"This CASA Airworthiness Directive requires owners/operators and maintainers of certain Bell 427 helicopters to inspect and, where necessary, remove tail‑rotor driveshaft disc assemblies manufactured Nov 2005–Nov 2006 that may have incorrect thickness or improper indexing.  \n\nIt mandates prompt checks, removal of non‑conforming or misaligned discs, logbook entries, and bars installation of noncompliant parts to prevent failure of the tail‑rotor driveshaft and potential loss of directional control."},"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"},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"This AD implements a focused safety correction tied to a specific manufacturing date range and a single part number. It enforces inspection, removal, and an installation prohibition to address the manufacturing defect identified by Transport Canada. The measure remains within the original purpose (remedying potentially defective disc assemblies) and does not broaden the scope beyond that safety objective."},"complexity_factors":["Applicability limited to specific helicopter serial number ranges (S/N up to 56056 and 58001–58002) and a single part number (P/N 407-340-340-103).","Manufacturing-date window condition (1 Nov 2005 – 30 Nov 2006) creates a temporal filter on affected parts.","Numeric tolerance specification for disc thickness (0.115–0.127 inch / 2.921–3.225 mm) requires measurement procedures and calibrated tools.","Multiple distinct requirements with different compliance timeframes (25 flight hours/30 days; 10 flight hours; 300 flight hours/next inspection; immediate install prohibition).","Cross-reference to an external technical document (BHTC ASB-427-07-17) and any later approved revisions — compliance depends on that ASB’s procedures and any future revisions.","Reference to an external regulator’s directive (Transport Canada AD CF-2007-14) adds an extra external linkage to interpretive material.","Recordkeeping obligation (log-book entry) for cases where no corrective action is required.","Procedural conditionality: if parts pass verification or are outside the manufacturing-date window no further action; otherwise removal or prohibition applies."],"plain_english_summary":"**What this directive does (mechanically)**\n\n- This Airworthiness Directive (AD) orders owners/operators of certain Bell 427 helicopters to inspect specific tail-rotor driveshaft disc assemblies (part number 407-340-340-103) and, where necessary, remove or not reinstall non-compliant discs. The AD requires following the inspection and corrective-action steps set out in Bell (BHTC) Alert Service Bulletin ASB-427-07-17 (or any later approved revision) (Requirement 1). \n\n- If a disc assembly passes the verification or its manufacturing date is outside 1 Nov 2005 – 30 Nov 2006, the operator must make a log‑book entry and no further action is required (Requirement 1). \n\n- If a disc is outside the specified thickness range (0.115–0.127 inch / 2.921–3.225 mm) it must be removed (Requirement 2). If a disc is not properly indexed it must be removed (Requirement 3). Operators are prohibited from installing the listed part number into any helicopter unless it is compliant with the ASB (Requirement 4).\n\n**Who is affected**\n\n- Owners/operators and maintenance organisations responsible for Bell Helicopter Textron Canada (BHTC) Model 427 helicopters with serial numbers up to 56056 and 58001 through 58002 that are fitted with disc assemblies P/N 407-340-340-103 (Applicability).\n\n**Deadlines and timing (how quickly this must be done)**\n\n- Initial verification (Requirement 1): within 25 flight hours or 30 days from the effective date of the AD, whichever comes first, unless already done (Compliance 1).\n- Removal of discs outside thickness tolerance (Requirement 2): within 10 flight hours after completing Requirement 1 (Compliance 2).\n- Removal for improper indexing (Requirement 3): within 300 flight hours or at the next scheduled inspection, whichever comes first, after completing Requirement 1 (Compliance 3).\n- The installation prohibition (Requirement 4) is immediate from the AD’s effective date (Compliance 4).\n\n**Why the regulator did this (stated reason)**\n\n- Transport Canada determined that discs of P/N 407-340-340-103 manufactured between 1 Nov 2005 and 30 Nov 2006 may have incorrect thickness or incorrect indexing, which could affect the tail rotor driveshaft (Background). The AD enforces inspection and removal to address that identified manufacturing issue.\n\n**Who pays, who decides, and how behaviour changes**\n\n- Operators bear the direct costs (inspection labour, measurement tools if not already held, log‑book work, removal and replacement parts if discs are non‑compliant, and associated aircraft downtime). Maintenance organisations perform the inspections and removals in accordance with the ASB (Requirement 1 and Requirement 2–3).\n\n- The regulator (Civil Aviation Safety Authority via this AD) mandates the action and accepts compliance with the referenced manufacturer’s ASB as the method of compliance (Requirement 1 and Note). The AD prevents installing the listed part unless it meets the ASB’s requirements (Requirement 4).\n\n- The practical change of behaviour is routine: affected helicopters must be inspected promptly; non‑conforming discs must be removed; operators must not install the specified P/N unless verified compliant; and a log‑book entry is required when no corrective action is necessary (Requirement 1).\n\n**Implementation, costs and risks**\n\n- Cost items: inspection time, potential replacement disc purchase, labour for removal/installation, aircraft out-of-service time, and record-keeping. These are paid by operators/owners or by their maintenance providers under contract.\n\n- Implementation risks: availability of replacement or compliant discs; potential scheduling congestion for maintenance facilities if many helicopters are affected; the need for accurate measurement and indexing checks per the ASB; and the administrative requirement to make and retain log‑book entries showing compliance. The AD references the manufacturer’s ASB and a Transport Canada AD (CF-2007-14), so operators must ensure they use the latest approved revisions of those documents (Requirement 1, Note).\n\n**Trade-offs and incentives**\n\n- The AD trades operator cost and downtime for removal of a potential in-service safety risk identified by the regulator. Compliance reduces the risk of tail‑rotor driveshaft problems arising from out-of-tolerance or mis-indexed discs. The requirement to follow the ASB channels work through recognised maintenance/repair procedures rather than leaving operators to invent verification methods.\n\n(References: Applicability; Requirements 1–4; Compliance paragraphs 1–4; Background.)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-427-6-disc-assemblies-tail-rotor-driveshaft","history":"/api/acts/ad-bell-427-6-disc-assemblies-tail-rotor-driveshaft/history","analysis":"/api/acts/ad-bell-427-6-disc-assemblies-tail-rotor-driveshaft/analysis","conflicts":"/api/acts/ad-bell-427-6-disc-assemblies-tail-rotor-driveshaft/conflicts","importantCases":"/api/acts/ad-bell-427-6-disc-assemblies-tail-rotor-driveshaft/important-cases","documents":"/api/acts/ad-bell-427-6-disc-assemblies-tail-rotor-driveshaft/documents"}}