{"id":"F2006B04566","name":"AD/BELL 212/35 - Tail Rotor Trunnion Bearing Housing","slug":"ad-bell-212-35-tail-rotor-trunnion-bearing-housing","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":114296,"registerId":"commonwealth-F2006B04566-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BELL 212/35 - Tail Rotor Trunnion Bearing Housing","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nBell Helicopter Textron 212 Series Helicopters\n\nAD/BELL 212/35 Tail Rotor Trunnion Bearing Housing 9/86\n\nDM\n\nApplicability: All model 212 S/N: 30501 to 30999 31101 to 31273 and 31275 32101 to 32142\n\n32201 to 32262.\n\nRequirement: Action in accordance with Bell Alert Service Bulletin No. 212-86-39, Revision A.\n\nCompliance: Part I of the Requirement Document: Within 25 hours time in service or seven days whichever occurs first after 6 August 1986 and thereafter at intervals not exceeding 25 hours time in service or 7 days, whichever occurs first, until Part II is complied with.\n\nPart II of the Requirement Document: Within 150 hours time in service or 60 days whichever occurs first after 31 July 1986.\n\nBackground: A trunnion bearing housing end web has been found below specified dimensions.\n\nFailure of the housing caused excessive tail rotor vibration and loss of control.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"The directive narrows regulatory obligations to a specific subset of Bell 212 helicopters identified by serial number and imposes additional mandatory maintenance requirements on those identified airframes. Mechanically, it introduces a temporary recurring inspection regime (Part I) followed by a required corrective action (Part II) within defined flight-hour or day limits; this represents a change in the maintenance and operational obligations for the affected aircraft compared with normal, non-directive operation. (Applicability; Requirement; Compliance)"},"complexity_factors":["Multiple specific serial-number ranges listed in Applicability, requiring precise identification of affected airframes","Two-part compliance regime (Part I recurring short-interval inspections, Part II definitive corrective action) with different deadlines","Deadlines given as either flight hours or calendar days (whichever occurs first), creating dual tracking requirements","Mandated compliance references an external document (Bell Alert Service Bulletin No. 212-86-39, Revision A), so operators must obtain and follow that bulletin","No alternative compliance pathway or exemptions are set out in the text provided, limiting operational discretion","Safety-critical consequence (loss of control) increases enforcement and operational impact of non-compliance","Repeated inspections until Part II is completed create ongoing administrative and maintenance scheduling burden"],"plain_english_summary":"What this instrument does (mechanically):\n\n- It requires operators of specific Bell Helicopter Textron Model 212 helicopters (listed by serial number) to carry out inspections and follow remedial actions set out in Bell Alert Service Bulletin No. 212-86-39, Revision A. (Applicability; Requirement)\n- The mandatory actions are split into two parts: Part I is a short-term recurring inspection regimen to be done within 25 hours time-in-service or seven days, whichever comes first, after 6 August 1986 and then repeated at the same intervals until Part II is completed. Part II must be completed within 150 hours time-in-service or 60 days, whichever occurs first, after 31 July 1986. (Compliance)\n\nWho is affected and who decides:\n\n- Affected parties are the owners/operators and maintenance organisations responsible for Bell 212 helicopters with the serial numbers listed in the Applicability section. (Applicability)\n- The Civil Aviation Safety Authority (CASA) issued the directive and requires compliance. The specific inspection and repair procedures to be followed are those set out by the helicopter manufacturer in the cited Bell Alert Service Bulletin. (Requirement)\n\nWhy the directive was issued (stated rationale):\n\n- The Background section reports that a tail rotor trunnion bearing housing end web was found below specified dimensions. Failure of that housing has caused excessive tail rotor vibration and loss of control. The directive implements the manufacturer’s corrective actions to address that risk. (Background)\n\nWho pays, what changes in behaviour, and operational effects:\n\n- Owners/operators bear the direct costs: inspection labour, any parts and repairs required by the service bulletin, and aircraft downtime while inspections or repairs are carried out. (Requirement; Compliance)\n- Maintenance behaviour changes include: scheduling and performing frequent inspections under Part I until the more definitive corrective action in Part II is completed; following the manufacturer’s service bulletin as the mandated method of compliance. (Requirement; Compliance)\n- The directive increases near-term maintenance workload because Part I inspections must be repeated every 25 flight hours or seven days (whichever is first) until Part II is done. Completing Part II removes the need for the recurring Part I inspections once complied with. (Compliance)\n\nCompliance burden, discretion, and implementation risk:\n\n- The AD makes compliance mandatory; the text references only the Bell Alert Service Bulletin as the required action. No alternative compliance route or exemption is stated in the instrument itself, so operators must follow the specified bulletin unless they obtain separate approval outside the text provided. (Requirement)\n- Implementation risk from non-compliance is described in the Background: failure of the housing may cause excessive tail-rotor vibration and loss of control. Completing the inspections and remedial actions in accordance with the service bulletin is the mechanism the AD prescribes to mitigate that risk. (Background; Requirement)\n\nCosts, incentives and trade-offs (mechanical and economic):\n\n- The directive imposes concentrated, identifiable costs on operators of the specified serial-number helicopters: recurring inspection costs and the one-off cost of the Part II corrective action. (Compliance)\n- Those costs create an incentive for operators to prioritise affected aircraft for inspection and repair, and to source the required parts and labour. The directive does not itself specify who supplies parts or carries out repairs; that will be determined by market choices and any approvals for maintenance providers. (Requirement)\n\nNotes on scope and implementation mechanics:\n\n- The AD applies only to a defined set of serial numbers listed under Applicability; it does not purport to apply to all Model 212 helicopters. (Applicability)\n- The AD implements the manufacturer’s Alert Service Bulletin as the required compliance method and sets short interim inspection intervals (Part I) followed by a final corrective action (Part II) within a longer window. (Requirement; Compliance)\n\nCited source text: Applicability; Requirement; Compliance; Background."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive addressing a specific mechanical defect in specific aircraft. It has not expanded beyond its original purpose of mandating inspection and repair of the tail rotor trunnion bearing housing defect."},"complexity_factors":["Single, specific mechanical defect addressed","Clear applicability list (specific serial number ranges)","Straightforward two-part compliance schedule with simple time/flight hour triggers","No defined terms section — uses standard aviation terminology","No cross-references to other legislation beyond the parent Civil Aviation Regulations 1998","Single external reference to Bell Alert Service Bulletin 212-86-39 Revision A","No conditional logic, exceptions, or nested provisions"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for specific Bell 212 helicopters.\n\n**What it does:**\n- Requires owners and operators of certain Bell 212 helicopters (serial numbers 30501–30999, 31101–31273, 31275, 32101–32142, and 32201–32262) to inspect and fix a dangerous defect in the **tail rotor trunnion bearing housing** — a critical part that helps control the helicopter's tail rotor.\n\n**Why it matters:**\n- A housing with an end web below specified dimensions can fail, causing **excessive tail rotor vibration and loss of control** — which could crash the helicopter.\n\n**What must be done:**\n- **Immediate action (Part I):** Within 25 flight hours or 7 days (whichever comes first) after 6 August 1986, and then repeated every 25 flight hours or 7 days until Part II is done.\n- **Permanent fix (Part II):** Within 150 flight hours or 60 days (whichever comes first) after 31 July 1986.\n\n**Who must follow this:**\n- Anyone operating the specified Bell 212 helicopter models — this is not optional. Compliance is mandatory under civil aviation law."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-212-35-tail-rotor-trunnion-bearing-housing","history":"/api/acts/ad-bell-212-35-tail-rotor-trunnion-bearing-housing/history","analysis":"/api/acts/ad-bell-212-35-tail-rotor-trunnion-bearing-housing/analysis","conflicts":"/api/acts/ad-bell-212-35-tail-rotor-trunnion-bearing-housing/conflicts","importantCases":"/api/acts/ad-bell-212-35-tail-rotor-trunnion-bearing-housing/important-cases","documents":"/api/acts/ad-bell-212-35-tail-rotor-trunnion-bearing-housing/documents"}}