{"id":"F2006B02545","name":"AD/AT/17 Amdt 3 - Vertical Fin Front and Rear Spars","slug":"ad-at-17-amdt-3-vertical-fin-front-and-rear-spars","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41801,"registerId":"commonwealth-F2006B02545-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AT/17 Amdt 3 - Vertical Fin Front and Rear Spars","content":"![](image.001.png)\n\n![](image.001.png)  \nAIRWORTHINESS DIRECTIVE\n\nFor the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/AT/17 Amdt 2 and issues the following AD under subregulation 39.1 (1) of CAR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.\n\n![](image.001.png)  \n\nAirtractor AT 300, 400 and 500 Series Aeroplanes\n\nAD/AT/17\n\nAmdt 3\n\n  \nVertical Fin Front and Rear Spars 3/2003\n\nApplicability: All Airtractor models AT-300, 400 and 500 series which do not incorporate the fin front spar attachment fitting steel reinforcement plate in accordance with Snow Engineering Service Letter SL #138, SL#155 and SL #196, as applicable. AT301 model S/Ns 301-0100 to 301-0736 must comply with SL#196.\n\nRequirement: 1. Inspect the vertical fin front spar attachment fitting as detailed in Snow Engineering Service Letters SL #138, SL#155 and SL #196, as applicable.\n\n    2. For aircraft listed in the Models and Serial Numbers section of SL#138, SL #155 or SL#196, modify by installing the fin front spar steel reinforcement plate in accordance with SL#138, SL #155 or SL#196, respectively.\n\nNote 1: FAA ADs 97-14-05, 2000-11-05 and NPRM No. 2000-CE-59-AD refer.\n\nNote 2: FAA AD 2000-11-05 added additional serial numbers to the applicability of SL# 196.\n\nCompliance: For Requirement 1:\n\n    If SL #138 is applicable, then unless already accomplished, initially inspect within the next 25 hours time in service, thereafter, re-inspect at intervals not exceeding 25 hours time in service.\n\n    b. If SL#155 is applicable, then unless already accomplished, initially inspect prior to exceeding 2000 hours time in service, or within 25 hours time in service after 20 March 2003, whichever occurs later. Thereafter, re-inspect at intervals not exceeding 100 hours time in service.\n\n    c. If SL#196 is applicable, then unless already accomplished, initially inspect prior to exceeding 4000 hours time in service, or within 25 hours time in service after 20 March 2003, whichever occurs later. Thereafter, re-inspect at intervals not exceeding 100 hours time in service.\n\nFor requirement 2: Before further flight following the discovery of cracking. This Amendment becomes effective on 20 March 2003.\n\nAirtractor AT 300, 400 and 500 Series Aeroplanes\n\nAD/AT/17 Amdt 3 (Continued)\n\nBackground: The initial issue of this AD was the result of in-flight incidents in the USA resulting in partial separation of the fin from the aircraft. Investigations found that the 3/16 inch thick aluminium alloy front spar attachment plate had failed through fatigue.\n\nSnow Engineering SL #138 introduced a recurring inspection and a terminating modification (steel attachment plate) which was mandated by the AD. Subsequently, an incident occurred where a 1/4 inch aluminium attachment fitting failed in identical circumstances. Amendment 1 expanded the applicability of the AD to all aircraft.\n\nThe terminating modification of SL #138 was applicable to a limited range of models and serial numbers only.\n\nSnow Engineering has now issued SL #196 which expands the aircraft serial number applicability for the inspections and terminating modification. The FAA has issued AD 2000-11-05 which requires inspection of unmodified aircraft at 100 hour intervals rather than 25 hours as previously.\n\nAmendment 3 expands the applicability to all the aircraft models listed in Snow Engineering SL #155 which were not covered by the other SL’s. The FAA has issued NPRM No. 2000-CE-59-AD to cover the serial numbers listed in SL#155 which are not covered by the other SLs and FAA ADs.\n\nAmendment 2 of this Airworthiness Directive became effective on 7 September 2000\\. Amendment 1 of this Airworthiness Directive became effective on 2 October 1996.\n\nThe original issue of this Airworthiness Directive became effective on 11 December 1995.\n\n![](image.002.png)  \n\nDavid Alan Villiers\n\nDelegate of the Civil Aviation Safety Authority 7 February 2003\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 26 February 2003.","sortOrder":0}],"analysis":{"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"},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":true,"description":"The original AD addressed a specific fatigue failure in 3/16 inch aluminium attachment plates for limited serial numbers. Through three amendments, the scope has expanded significantly: Amendment 1 expanded to all aircraft; Amendment 2 incorporated expanded serial number coverage via SL #196; Amendment 3 now covers additional models via SL #155 that were not covered by previous service letters. The directive has grown from addressing a specific part failure in specific aircraft to a comprehensive regime covering three aircraft series with multiple service bulletins, three different inspection intervals, and terminating modifications across an expanded fleet."},"complexity_factors":["Multiple overlapping applicability criteria based on aircraft model, serial number ranges, and whether specific modifications have already been performed","Three different service letters (SL #138, SL #155, SL #196) with distinct inspection intervals and thresholds that must be cross-referenced to determine compliance obligations","Conditional compliance timing ('whichever occurs later' calculations involving flight hours and calendar dates)","Nested exceptions: 'unless already accomplished' clauses modify the primary obligations","External document incorporation by reference (FAA ADs and Snow Engineering Service Letters not reproduced in full)","Amendment history tracking (references to Amendments 1, 2, and original issue with different effective dates)"],"plain_english_summary":"This safety order requires owners/operators of Airtractor AT‑300/400/500 crop‑dusters to inspect the vertical tail fin for fatigue cracking at prescribed intervals and to install a steel reinforcement plate if cracks are found; aircraft may not fly until repaired. \n\nAmendment 3 expands covered models, mandates recurring inspections until the permanent steel fix is fitted, and became enforceable on 20 March 2003."},"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"The directive has broadened in scope since the original issue. The original AD targeted a limited set of models/serial numbers after specific failures; subsequent amendments (including this Amendment 3) expanded applicability to additional serial numbers and models by incorporating Snow Engineering SL #155 and SL #196. The amendment also aligns inspection intervals with later FAA guidance (changing some recurring inspections from 25‑hour intervals to 100‑hour intervals for unmodified aircraft under certain SLs). In short, the AD moved from a narrowly targeted set of affected aircraft to cover a wider set of Airtractor AT‑300/400/500 aeroplanes that lack the steel reinforcement plate, thereby increasing the number of operators required to perform recurring inspections or the terminating modification."},"complexity_factors":["Three separate Snow Engineering Service Letters (SL #138, SL #155, SL #196) are referenced and determine different obligations","Different inspection regimes conditional on which SL applies (25‑hour vs 100‑hour intervals)","Initial inspection timing uses nested conditions (either before exceeding X hours TIS or within 25 hours after 20 March 2003, whichever is later)","Serial‑number specific applicability (including a specific AT-301 S/N range) increases record‑checking required","Terminating modification (installation of steel plate) removes recurring inspection for aircraft where it is applicable, adding a conditional end state","Cross‑references to external FAA ADs and an FAA NPRM (adds external regulatory dependency)","Short re‑inspection intervals (as low as 25 flight hours) create operational complexity in scheduling and maintenance","Notes and historical amendments imply changes over time that operators must reconcile with current status"],"plain_english_summary":"**What this instrument is**\n\n- This is an Airworthiness Directive (a mandatory safety order for aircraft) that applies to Airtractor AT-300, AT-400 and AT-500 series aeroplanes. (An Airworthiness Directive legally requires operators to take specified inspections or repairs to fix an identified unsafe condition.)\n\n**What it requires (mechanics of the rule)**\n\n- Applicability (Applicability section): It applies to all Airtractor AT-300/400/500 aeroplanes that do not already have a steel reinforcement plate fitted to the vertical fin front spar attachment fitting. A specific serial‑number range for the AT-301 is called out to comply with Snow Engineering Service Letter (SL) #196.\n\n- Inspections (Requirement 1; Compliance section): Operators must inspect the vertical fin front spar attachment fitting in the way described in the relevant Snow Engineering Service Letter (SL #138, SL #155 or SL #196). Which SL applies depends on the aircraft model/serial number.\n\n- Modification (Requirement 2): For aircraft listed in the Models and Serial Numbers sections of the applicable SL, operators must fit (modify by installing) the steel reinforcement plate specified in the applicable SL.\n\n- Timings (Compliance section): The inspection schedule depends on which SL applies:\n  - If SL #138 applies: initial inspection within the next 25 flight hours unless already done, then every 25 hours thereafter.\n  - If SL #155 applies: initial inspection before exceeding 2,000 hours total time‑in‑service, or within 25 hours after 20 March 2003 (whichever is later), then every 100 hours thereafter.\n  - If SL #196 applies: initial inspection before exceeding 4,000 hours total time‑in‑service, or within 25 hours after 20 March 2003 (whichever is later), then every 100 hours thereafter.\n  - If cracking is found: the steel reinforcement modification must be installed before further flight.\n\n- Effective date: the amendment takes effect 20 March 2003 (Compliance/introductory lines).\n\n**Why the rule exists (stated background and technical trigger)**\n\n- Background section: The directive stems from in‑flight incidents in the USA where part of the vertical fin partially separated because the aluminium front spar attachment plate failed from fatigue. Snow Engineering originally issued SL #138 (introducing recurring inspections and a terminating modification: the steel plate). Subsequent failures and expanded serial‑number findings led to additional SLs (#155 and #196) and expanded applicability. The FAA has issued related ADs and a proposed rule referenced in the AD.\n\n**Who is affected and who pays**\n\n- Affected parties: aircraft owners/operators of the specified Airtractor models that do not already have the steel reinforcement plate fitted; maintenance organisations that perform the inspections and modifications.\n\n- Who pays: owners/operators must pay for the recurring inspections, any required repairs, and the cost and labour to install the steel reinforcement plate when required. There will also be aircraft downtime (loss of use) while inspections or modifications are carried out.\n\n**Behavioural and market effects, implementation issues and trade‑offs**\n\n- Safety vs cost: the AD forces additional recurring maintenance or a one‑time modification (the steel plate). The modification is described as a \"terminating modification\" in the background (it stops the need for the recurring inspection for aircraft to which it properly applies). That creates a trade‑off: pay once for the modification to stop frequent inspections or continue to incur inspection costs and operational limits.\n\n- Concentrated benefits and diffuse costs: benefits (reduced risk of fin failure) accrue to operators and their passengers; the immediate costs are concentrated on affected aircraft owners/operators who must pay for inspections/mods.\n\n- Compliance burden and implementation risk: multiple different SLs and serial‑number rules mean operators must check which SL applies to each airframe. Short re‑inspection intervals in some cases (as short as every 25 hours) create high operational burden and may cause scheduling or availability issues. Availability of approved reinforcement plates and qualified maintenance resources may constrain how quickly operators can do the terminating modification.\n\n- Incentives: owners of high‑utilisation aeroplanes face higher inspection costs (more frequent inspections) unless they install the plate. Installing the plate reduces ongoing inspection cost and operational interruption; operators will weigh that against upfront modification cost and downtime.\n\n- Interaction with other regulators: the AD cross‑references FAA ADs and an FAA NPRM; operators that fly internationally must track both CASA (Australian) and FAA requirements where applicable.\n\n**Where to look in the instrument**\n\n- Applicability section: which aircraft are in scope.\n- Requirement section (items 1 and 2): what to inspect and what to modify.\n- Compliance section: timing and intervals for inspections and the requirement to fit the plate before further flight if cracking is found.\n- Background section: factual history and relation to Snow Engineering SLs and FAA ADs.\n\n(References: the AD’s Applicability, Requirement, Compliance and Background sections.)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-at-17-amdt-3-vertical-fin-front-and-rear-spars","history":"/api/acts/ad-at-17-amdt-3-vertical-fin-front-and-rear-spars/history","analysis":"/api/acts/ad-at-17-amdt-3-vertical-fin-front-and-rear-spars/analysis","conflicts":"/api/acts/ad-at-17-amdt-3-vertical-fin-front-and-rear-spars/conflicts","importantCases":"/api/acts/ad-at-17-amdt-3-vertical-fin-front-and-rear-spars/important-cases","documents":"/api/acts/ad-at-17-amdt-3-vertical-fin-front-and-rear-spars/documents"}}