{"id":"F2006B04667","name":"AD/BELL 412/33 - Main Transmission Lower Planetary Spider","slug":"ad-bell-412-33-main-transmission-lower-planetary-spider","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44419,"registerId":"commonwealth-F2006B04667-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BELL 412/33 - Main Transmission Lower Planetary Spider","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 412 Series Helicopters\n\nAD/BELL 412/33 Main Transmission Lower Planetary Spider 2/95\n\nApplicability: All Bell Helicopter Textron 412 Series Helicopters with main transmission lower planetary spider P/N 412-040-785-101 installed.\n\nRequirement: Retire the spider from service.\n\nNote 1: FAA AD 94-18-09 Amdt 39-9022 and Bell Alert Service Bulletin ASB 412- 93-72 Revision A refer.\n\nNote 2: The life of Spider P/N 412-040-785-103 is not affected by this AD.\n\nCompliance: Retire the spiders before accumulating 2500 hours time in service or within 100 hours time in service after 2 February 1995, whichever is the later.\n\nBackground: Five failures of the main transmission lower planetary spider have been experienced during the manufacturer’s fatigue tests. Accordingly a fatigue life has been established to prevent in service failures.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive’s scope aligns with its stated purpose in the text: it targets one specific part number (P/N 412-040-785-101) and requires retirement at a defined life limit to address fatigue failures observed in testing. The AD explicitly excludes P/N 412-040-785-103, and it cross-references FAA and manufacturer service documents for implementation. There is no textual indication that the directive changes scope beyond that original, stated intent."},"complexity_factors":["Narrow applicability limited to a single specific part number (P/N 412-040-785-101) increases clarity but requires precise recordkeeping (Applicability).","Mandatory retirement with a hard hours limit (2,500 hours) and a contemporaneous window (within 100 hours after 2 February 1995) requires operators to track part time-in-service accurately (Compliance).","Cross-reference to external documents (FAA AD and Bell Alert Service Bulletin) means operators must consult additional technical guidance to implement removals correctly (Note 1).","Explicit carve-out for a closely numbered part (P/N 412-040-785-103) adds an extra compatibility/interpretation check for maintenance planners (Note 2).","Technical rationale (fatigue failures during manufacturer testing) is concise but implies a safety risk if not complied with, increasing operational urgency (Background)."],"plain_english_summary":"What this instrument does mechanically:\n\n- Applicability: It applies to all Bell Helicopter Textron 412 series helicopters that have the main transmission lower planetary spider part number 412-040-785-101 installed. (Applicability)\n- Mandatory action: Those specific spiders must be removed from service (retired). (Requirement)\n- Timing: Retirement must occur before the part accumulates 2,500 hours time-in-service, or within 100 hours time-in-service after 2 February 1995, whichever is later. Operators must schedule removals to meet that deadline. (Compliance)\n- Cross-references: The directive notes related FAA and manufacturer service documents that provide further detail. (Note 1)\n- Limited scope: A closely numbered part, P/N 412-040-785-103, is explicitly not affected by this directive. (Note 2)\n- Rationale given: The retirement requirement follows five failures of this spider during manufacturer fatigue testing, so a fatigue life limit was set to reduce the risk of in‑service failure. (Background)\n\nWho pays, who decides, and what changes in behaviour:\n\n- Who decides: The Civil Aviation Safety Authority issues the directive and sets the mandatory retirement requirement. (header/Requirement)\n- Who pays: Operators that own or operate affected Bell 412 helicopters are the parties that bear the direct costs of compliance — they must remove the listed spider from service and, if necessary, obtain and install a replacement component. (Applicability, Requirement, Compliance)\n- Behaviour changes required: Operators must monitor part hours, schedule the component’s retirement by the deadline, perform the removal, and keep maintenance records showing compliance. (Compliance)\n\nCosts, incentives and trade-offs (mechanically stated):\n\n- Direct costs: removal labour, inspection, possible replacement-part purchase, and associated aircraft downtime are concrete costs imposed on affected operators. (Applicability, Requirement, Compliance)\n- Compliance burden: Tracking the specific part’s hours and meeting the retirement window creates administrative and operational scheduling requirements. (Compliance)\n- Implementation risk: If an operator does not retire the part within the specified hours or window, the stated safety risk (fatigue failure) remains. (Background, Compliance)\n- Bureaucratic discretion: The directive gives a clear rule (retire at or before 2,500 hours or within 100 hours after the specified date) and leaves little operational discretion about whether to retire the listed P/N; notes point operators to related FAA and manufacturer documents for technical detail. (Requirement, Compliance, Note 1)\n\nEffects on private enterprise and markets (source-grounded):\n\n- Competition and contract freedom: The directive constrains operator choices about how long to operate a specific part number; it does not itself mandate any particular supplier or replacement, and it excludes P/N 412-040-785-103 from the requirement. (Requirement, Note 2)\n- Prices and supply: The AD may raise demand for replacement components or overhaul services for affected helicopters, creating procurement and price pressure for operators; this follows mechanically from requiring retirement of a widely used part number. (Requirement, Compliance)\n\nConcentrated benefits and diffuse costs (mechanical view):\n\n- Benefit concentration: The safety benefit of reduced risk of part failure accrues to operators, their passengers, and the public; the directive is targeted at a single part number identified by testing. (Background, Applicability)\n- Cost dispersion: The compliance costs fall on the set of operators using the affected spider; those not using it are unaffected. (Applicability, Requirement)\n\nNotes on interaction with other documents:\n\n- The AD points to an FAA airworthiness directive and a Bell alert service bulletin for related technical instructions; operators will likely consult those documents to carry out removals and related inspections. (Note 1)\n\nOverall mechanical effect: The directive requires operators of Bell 412 helicopters fitted with P/N 412-040-785-101 to retire that part by a stated hours limit or within a short window after a specified date, on the stated basis that fatigue testing showed failures and a finite life must be enforced to avoid in‑service failure. (Requirement, Compliance, Background)"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, single-issue safety directive targeting one specific defective part. It has not expanded beyond its original purpose of grounding a faulty component."},"complexity_factors":["Single, unambiguous operative requirement ('Retire the spider from service')","Only one defined term of note ('time in service')","Simple binary applicability test (specific part number installed or not)","Clear compliance deadline with straightforward 'whichever is later' logic","No cross-references to other legislation sections — only non-binding references to FAA documents and manufacturer bulletins in notes","Extremely short document (under 200 words)"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA).\n\n**What it does:**\nOrders the immediate retirement (permanent removal from use) of a specific helicopter part — the \"main transmission lower planetary spider\" — on all Bell 412 series helicopters.\n\n**Who it affects:**\nOwners and operators of Bell 412 helicopters that have the specific part number **412-040-785-101** installed in their main transmission system.\n\n**Why it matters:**\nThe manufacturer found this part was failing in fatigue tests (tests that simulate repeated stress over time). Five failures occurred during testing, meaning the part could break in actual flight with potentially catastrophic consequences. To prevent crashes, CASA has set a hard deadline: the part must be removed after **2,500 flight hours** or within **100 flight hours after 2 February 1995** — whichever gives more time.\n\n**Key points:**\n- This is **not optional** — compliance is legally mandatory\n- A different part number (412-040-785-103) is **not affected** — only the -101 version\n- The directive references equivalent US FAA rules and manufacturer bulletins for technical details"}},"importantCases":[],"_links":{"self":"/api/acts/ad-bell-412-33-main-transmission-lower-planetary-spider","history":"/api/acts/ad-bell-412-33-main-transmission-lower-planetary-spider/history","analysis":"/api/acts/ad-bell-412-33-main-transmission-lower-planetary-spider/analysis","conflicts":"/api/acts/ad-bell-412-33-main-transmission-lower-planetary-spider/conflicts","importantCases":"/api/acts/ad-bell-412-33-main-transmission-lower-planetary-spider/important-cases","documents":"/api/acts/ad-bell-412-33-main-transmission-lower-planetary-spider/documents"}}