{"id":"F2005L02087","name":"AD/AT/26 - Horizontal Stabiliser Attachment Eyebolts","slug":"ad-at-26-horizontal-stabiliser-attachment-eyebolts","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":36305,"registerId":"commonwealth-F2005L02087-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Airtractor AT-300, 400 and 500 Series Ae","sectionType":"division","heading":"Airtractor AT-300, 400 and 500 Series Aeroplanes","content":"### Airtractor AT-300, 400 and 500 Series Aeroplanes\n\n| AD/AT/26 | Horizontal Stabiliser Attachment Eyebolts | 9/2005 |\n| -------- | ----------------------------------------- | ------ |\n\n| Applicability: | Models AT-300, AT-301, AT-302, AT-400, and AT-400A aircraft; all serial numbers.Model AT-401/AT-402 aircraft, with serial numbers up to and including 401-0700.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |\n| -------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | 1. Tighten the four eyebolts that attach the front and rear spar of the horizontal stabiliser to the respective stabiliser strut using the torque values referenced in Snow Engineering Co. Service Letter (SL) No. 129, revised 21 October 2004.2. Replace eyebolts that attach the front and rear spar of the horizontal stabiliser to the respective stabiliser strut, in accordance with SL No. 129, Issued 26 September 1994, Revised 21 October 2004.Do not install any 5/16-inch eyebolt (part number AN44-17A or AN44-21A), 7/16-inch eyebolt (AN47-22A or AN-47-30A), or 9/16-inch eyebolt (part number 30774-1 or 30775-1) that exceeds the corresponding cumulative hours time in service specified in Requirement 2 of this Directive.Note: FAA AD 2005-13-12 Amdt 39-14149 refers. |\n| Compliance:    | 1. Within 100 hours time in service or 12 calendar months after 1 September 2005, whichever occurs first, unless already accomplished. Tighten thereafter at intervals not to exceed 12 calendar months.2. Replace initially upon accumulating the applicable number of hours time in service specified in SL No. 129, revised 21 October 2004, or within 50 hours time in service after 1 September 2005, whichever occurs later. Replace thereafter at the intervals specified in SL No. 129, revised 21 October 2004.                                                                                                                                                                                                                                                                        |\n|                | This Airworthiness Directive becomes effective on 1 September 2005.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |\n\n| Background: | The FAA has received numerous reports of failures of horizontal stabiliser attachment eyebolts on AT-301, AT-400, and AT-602 aircraft. Engineering analysis concluded that the eyebolts failed as a result of high cycle, low-nominal stress; and most likely due to the loss of torque during service. Failure of an eyebolt could lead to an abrupt change or complete loss of pitch control and/or aircraft departure from controlled flight. |\n| ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n\n![](image.001.png)  \nDavid Villiers  \nDelegate of the Civil Aviation Safety Authority\n\n20 July 2005","sortOrder":0},{"sectionNumber":"AD/AT/26","sectionType":"part","heading":"AD/AT/26","content":"## AD/AT/26","sortOrder":1},{"sectionNumber":"Horizontal Stabiliser Attachment Eyebolt","sectionType":"part","heading":"Horizontal Stabiliser Attachment Eyebolts","content":"## Horizontal Stabiliser Attachment Eyebolts","sortOrder":2},{"sectionNumber":"9/2005","sectionType":"part","heading":"9/2005","content":"## 9/2005","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"This Directive implements a focused safety corrective action addressing reported eyebolt failures. It stays within that original corrective scope: requiring torque checks, replacement per an existing Service Letter, and prohibiting installation of specified part numbers past stated hours. It does not add unrelated obligations, broaden affected aircraft beyond the listed models/serial ranges, or repurpose the measure into a wider regulatory regime."},"complexity_factors":["Single-issue airworthiness directive focused on one component (eyebolts)","Applicability limited to a small set of Airtractor models and serial-number subset","Two principal mandated actions (tighten and replace) plus a prohibition on installing specified part numbers beyond cumulative hours","Relies on an external service letter (Snow Engineering SL No. 129 revised 21 Oct 2004) for technical specifics (torque values and hours-to-replace)","Conditional compliance windows (100 hours or 12 months; initial replacement at hours TIS or within 50 hours) creating branching timing rules","Explicit part-number list that requires component-level tracking","Cross-reference to FAA AD (additional external regulatory linkage)"],"plain_english_summary":"**What this directive does (mechanically)**\n\n- Applies to Airtractor models AT-300, AT-301, AT-302, AT-400, AT-400A (all serial numbers) and AT-401/AT-402 with serial numbers up to and including 401-0700 (see \"Applicability\").\n- Requires two maintenance actions on the four eyebolts that attach the front and rear spars of the horizontal stabiliser to their struts:\n  - **Tighten** the four eyebolts to the torque values specified in Snow Engineering Co. Service Letter (SL) No. 129 (revised 21 October 2004). (Requirement 1)\n  - **Replace** eyebolts in accordance with SL No. 129 (issued 26 Sept 1994, revised 21 Oct 2004). The Directive also prohibits installing certain eyebolt part numbers if they have exceeded the cumulative hours-in-service limits set out in Requirement 2. (Requirement 2)\n- Sets specific timing for compliance: tighten within 100 flight hours or 12 calendar months from 1 September 2005 (whichever is earlier) unless already done; thereafter re‑tighten at intervals not exceeding 12 months. Replace initially at the hours-in-service threshold in the Service Letter or within 50 flight hours after 1 September 2005 (whichever is later); then replace at the intervals in the Service Letter. (Compliance)\n- Effective date: becomes effective on 1 September 2005.\n\n**Why it was issued (stated reason)**\n\n- The FAA reported multiple failures of horizontal stabiliser attachment eyebolts on related Airtractor models. Engineering analysis attributed the failures to high-cycle, low-nominal stress made worse by loss of torque during service. A failed eyebolt can cause abrupt change or complete loss of pitch control and/or departure from controlled flight. (Background)\n\n**Who this affects and who pays**\n\n- Affected parties: aircraft owners/operators and maintenance organisations responsible for the listed Airtractor models and serial ranges.\n- Who pays: operators/owners pay for labour, parts, and any aircraft downtime required to accomplish the tightening and replacements.\n\n**How this changes behaviour and decisions**\n\n- Operators must institute (or confirm) a periodic eyebolt torque and replacement regime that follows Snow Engineering SL No. 129 and the timeframes in this Directive. Maintenance personnel must record hours time in service (TIS) for eyebolts to know when to replace them and must apply and verify specified torque values. Regulators may enforce compliance through routine surveillance, continuing airworthiness checks, or during certification/maintenance audits.\n\n**Practical costs, incentives and trade-offs**\n\n- Direct costs: labour to perform torque checks and replacements, the cost of replacement eyebolts, and aircraft downtime (opportunity cost of lost flying hours).\n- Incentives: the rule creates a clear incentive to track eyebolt hours and torque retention; operators may replace eyebolts earlier to reduce the risk of in-service failure, or increase inspection frequency to avoid premature replacement costs.\n- Implementation risks: accurate torque application and verification; reliable record-keeping of cumulative hours for each eyebolt; availability of replacement eyebolts (supply chain risk); and correct identification of part numbers and serial-tracked components.\n- Compliance burden: depends on current maintenance practices—operators already on an annual torque check and tracked parts program will have lower marginal burden. Smaller operators without strict component-hours tracking may face higher administrative and operational costs.\n\n**Dependencies, references and enforcement mechanics**\n\n- The Directive relies on an external technical document (Snow Engineering Co. SL No. 129, revised 21 Oct 2004) for the exact torque values and hours-to-replace criteria. This creates a dependency on that Service Letter for correct implementation (Requirement and Compliance sections).\n- The Directive specifically lists prohibited installation of certain part numbers (AN44-17A, AN44-21A, AN47-22A, AN-47-30A, 30774-1, 30775-1) once they exceed the cumulative hours TIS specified. That requires operators to track part numbers and cumulative hours for each eyebolt.\n- The Directive cross-references FAA AD 2005-13-12 (Amdt 39-14149), indicating alignment with FAA action but the required mechanical steps and timing are set by this Directive and the referenced Snow Engineering Service Letter.\n\n**Net effect**\n\n- Transfers the responsibility for reducing the risk of eyebolt fatigue failure onto ongoing maintenance practice: regular torque checks, record-keeping of hours for eyebolts, and replacement at specified intervals. The regulator enforces the requirement; operators bear the costs and must adapt maintenance planning and inventory management accordingly.\n\n(References: Applicability, Requirement, Compliance, Background sections of the Directive.)"},"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a standard Airworthiness Directive with a focused, single-purpose scope: addressing a specific mechanical failure mode in a defined aircraft fleet. The scope remains tightly constrained to horizontal stabiliser eyebolt maintenance and has not expanded beyond its original safety intent."},"complexity_factors":["Multiple applicability criteria (specific model numbers and serial number cut-offs)","Two distinct compliance actions with different deadlines (tightening vs replacement)","Cross-reference to external technical document (Snow Engineering Service Letter No. 129) for torque values and replacement intervals","Conditional logic in compliance dates ('whichever occurs first' / 'whichever occurs later')","Specific part number prohibitions with dimensional specifications","Dual measurement systems (flight hours vs calendar months)"],"plain_english_summary":"Owners/operators of certain Air Tractor crop-dusters (AT-300/400/500 series, plus early AT-401/402 serials) must inspect and maintain the eyebolts that secure the horizontal stabiliser. CASA requires timely torque checks, scheduled replacements, and bans installation of over‑used part‑numbered eyebolts to prevent in‑flight eyebolt failure. The AD addresses reported failures that can cause sudden pitch loss and potential crashes."}},"importantCases":[],"_links":{"self":"/api/acts/ad-at-26-horizontal-stabiliser-attachment-eyebolts","history":"/api/acts/ad-at-26-horizontal-stabiliser-attachment-eyebolts/history","analysis":"/api/acts/ad-at-26-horizontal-stabiliser-attachment-eyebolts/analysis","conflicts":"/api/acts/ad-at-26-horizontal-stabiliser-attachment-eyebolts/conflicts","importantCases":"/api/acts/ad-at-26-horizontal-stabiliser-attachment-eyebolts/important-cases","documents":"/api/acts/ad-at-26-horizontal-stabiliser-attachment-eyebolts/documents"}}