{"id":"F2006B04663","name":"AD/BELL 412/29 - Tail Rotor Driveshaft Hangar Bearings","slug":"ad-bell-412-29-tail-rotor-driveshaft-hangar-bearings","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44415,"registerId":"commonwealth-F2006B04663-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BELL 412/29 - Tail Rotor Driveshaft Hangar Bearings","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-generator: Aspose.Words for .NET 22.10.0\n---\n\n?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"no\"?>\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  Bell Helicopter Textron 412 Series Helicopters\n\n \n\nAD/BELL 412/29 Tail Rotor Driveshaft Hangar Bearings 1/92\n\nDM\n\nApplicability: All models fitted with tail rotor driveshaft bearings P/N 204-040-623-003 with S/N prefixed with either “T” or “N” prior to N4000.\n\n \n\nRequirement: Action in accordance with Bell Alert Service Bulletin 412-91-54 Revision A.\n\n \n\nNote: FAA Priority Letter AD 91-24-16 refers.\n\n \n\nCompliance: Daily before first flight of the day after 27 November 1991.\n\n \n\nBackground: A daily inspection of the tailrotor driveshaft bearings has been found necessary following a fatal accident which revealed the possibility of a production batch problem with these bearings.\n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The AD's wording confines its requirements to a narrowly defined set of bearings (P/N 204-040-623-003 with S/N prefixes “T” or “N” prior to N4000) and prescribes daily inspections and compliance with a specific Bell Alert Service Bulletin. The directive therefore appears to implement the original aim described in the text—to address a production-batch concern identified after a fatal accident—without broadening obligations beyond the identified parts and the actions in the ASB. (Applicability, Requirement, Compliance, Background)"},"complexity_factors":["Narrow, specific applicability limited to one part number and a defined serial-number range (Applicability)","Mandatory, high-frequency compliance requirement (daily, before first flight) that imposes recurring operational duties (Compliance)","Dependence on an external document (Bell Alert Service Bulletin 412-91-54 Revision A) for the substantive inspection and corrective actions (Requirement)","Safety-critical subject matter (tail rotor driveshaft bearings) which raises operational and liability sensitivity despite simple rule text (Background)","Cross-reference to an FAA Priority Letter AD, requiring operators to be aware of multiple regulatory sources (Note)"],"plain_english_summary":"CASA requires operators of Bell 412 helicopters fitted with tail‑rotor driveshaft bearings P/N 204‑040‑623‑003 (serials beginning with “T” or “N” before N4000) to perform a daily pre‑flight inspection per Bell Alert Service Bulletin 412‑91‑54 Rev A. Issued after a fatal accident suggesting a possible production‑batch defect, the AD shifts recurring inspection and any repair/replacement costs to operators and increases maintenance workload."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive issued in response to a specific accident. It has not grown beyond its original purpose of mandating daily inspections for a specific defective part batch."},"complexity_factors":["Very short document (approximately 150 words)","Only 2 defined terms (P/N for Part Number, S/N for Serial Number)","Single, clear requirement with no conditional logic or exceptions","No cross-references to other legislation sections — only references to external technical documents (service bulletin and FAA directive)","Straightforward applicability criteria using simple part/serial number ranges"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for aircraft.\n\n**What it does:**\nIt requires owners and operators of **Bell 412 series helicopters** to perform a **daily inspection** of specific tail rotor driveshaft bearings before the first flight each day.\n\n**Who it affects:**\n- Operators of Bell 412 helicopters fitted with particular bearing parts (P/N 204-040-623-003) with serial numbers starting with \"T\" or \"N\" below N4000.\n- This targets a specific production batch of bearings suspected of having a manufacturing defect.\n\n**Why it matters:**\nA fatal accident revealed these bearings could fail due to a production problem. The daily check is an emergency safety measure to catch potential failures before they cause another accident. The directive references a Bell Alert Service Bulletin and an FAA (US aviation authority) directive, showing international coordination on this safety issue.\n\n**Compliance deadline:**\nDaily inspections began being required from **27 November 1991**."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-412-29-tail-rotor-driveshaft-hangar-bearings","history":"/api/acts/ad-bell-412-29-tail-rotor-driveshaft-hangar-bearings/history","analysis":"/api/acts/ad-bell-412-29-tail-rotor-driveshaft-hangar-bearings/analysis","conflicts":"/api/acts/ad-bell-412-29-tail-rotor-driveshaft-hangar-bearings/conflicts","importantCases":"/api/acts/ad-bell-412-29-tail-rotor-driveshaft-hangar-bearings/important-cases","documents":"/api/acts/ad-bell-412-29-tail-rotor-driveshaft-hangar-bearings/documents"}}