{"id":"F2006B02551","name":"AD/AT/25 - Vertical Fin Front Spar Fitting","slug":"ad-at-25-vertical-fin-front-spar-fitting","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41807,"registerId":"commonwealth-F2006B02551-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"AIRWORTHINESS DIRECTIVE","sectionType":"part","heading":"AIRWORTHINESS DIRECTIVE","content":"# ![](image.001.png)  \nAIRWORTHINESS DIRECTIVE\n\nFor the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CASR 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","sortOrder":0},{"sectionNumber":"AD/AT/25 Vertical Fin Front Spar Fitting","sectionType":"part","heading":"AD/AT/25 Vertical Fin Front Spar Fitting 7/2003","content":"# AD/AT/25 Vertical Fin Front Spar Fitting 7/2003\n\nApplicability: Model AT-300, AT-400, and AT-400A aircraft equipped with a turbine powerplant, and retrofitted with a ¼-inch thick aluminium vertical fin front spar fitting and an all- metal rudder.\n\nModel AT-401 and AT-401B aircraft, serial numbers 401-0737 through 401-1015, and 401B-0737 through 401B-1015; that have been converted to turbine powerplants.\n\nModel AT-402, AT-402A, and AT-402B aircraft, serial numbers 402-0737 through 402B-1015.\n\nModel AT-501 aircraft, serial number 501-0031 and subsequent, tha t have been converted to turbine powerplants.\n\nModel AT-502 and AT-502B aircraft, serial numbers 502-0031 through 502B-0398.\n\nRequirement: 1. Inspect the vertical fin front spar fitting for cracks in accordance with Snow Engineering Co. Service Letter (SL) No. 155, Revised 27 November 2002.\n\n    2. If cracks are found during any inspection required by Requirement 1, replace the vertical fin front spar fitting in accordance with SL No. 155, Revised 27 November 2002.\n    3. Modify the vertical fin front spar fitting by installing a steel doubler in accordance with SL No. 155, Revised 27 November 2002.\n\nNote: FAA AD 2003-07-04, Amendment 39-13100 refers.\n\nCompliance: 1. Upon accumulating 2,000 hours time in service on the vertical fin front spar or spar fitting, or within 100 hours time in service after 10 July 2003, whichever occurs later. If no cracks are found, inspect thereafter at intervals not to exceed 100 hours time in service; until Requirement 3 is accomplished.\n\n    2. Before further flight.\n\n    3. Within 2,000 hours time in service after 10 July 2003, unless already accomplished. The modification may be accomplished at any time prior provided the vertical fin front spar fitting is crack free.","sortOrder":1}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive applies to the specific models and serial numbers listed and prescribes inspection, replacement and modification actions as stated. The text gives no indication that the AD expands scope beyond those enumerated aircraft or that it alters the underlying applicability from its stated form."},"complexity_factors":["Applicability lists multiple models and several serial‑number ranges, requiring operators to check eligibility precisely (Applicability).","Inspections, replacement and modification must follow an external document: Snow Engineering Service Letter No. 155 (Requirement 1–3), creating dependency on that technical publication.","Time‑based compliance windows with alternative triggers: 2,000 hours on the spar or within 100 hours after a specified date, and recurring 100‑hour inspections until modification (Compliance).","Immediate operational constraint if cracks are found: replacement is required before further flight, imposing potential grounding and scheduling costs (Requirement 2; Compliance 2).","A retrofit modification (steel doubler) is mandated within a 2,000‑hour window, but may be done earlier if the fitting is crack‑free, creating planning flexibility but added procurement and labour tasks (Requirement 3; Compliance 3).","Cross‑reference to FAA AD (Note) may require operators to reconcile international guidance with the Snow Engineering letter.","Administrative burden: recordkeeping of hours, inspections and compliance steps, and repeated inspections until modification is accomplished (Requirement 1; Compliance)."],"plain_english_summary":"This Airworthiness Directive requires owners/operators of specified Airtractor models (certain AT‑300/400/500 series and listed AT‑401/402/501/502 serial‑number variants) to inspect the vertical fin front spar fitting for cracks, replace cracked fittings, and install a steel doubler per Snow Engineering Service Letter No. 155 (rev. 27 Nov 2002).\n\nCompliance is time‑based (initial at 2,000 hours on the spar or within 100 hours after 10 July 2003, then 100‑hour intervals until modification; replace before further flight if cracks are found), so operators bear inspection, repair and modification costs and scheduling obligations."},"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":3,"scope_assessment":{"changed":false,"description":"This is a discrete safety directive targeting a specific mechanical defect in a defined aircraft fleet. It has not expanded beyond its original purpose of addressing the vertical fin front spar fitting cracking issue."},"complexity_factors":["Multiple applicability conditions combining model numbers, serial number ranges, engine types (turbine vs piston), and retrofit status","Three distinct requirements with different compliance triggers and timelines","Cross-reference to external technical document (Snow Engineering Service Letter 155) for actual inspection and modification procedures","Nested timing logic for compliance: 'whichever occurs later' clauses and conditional intervals","Reference to corresponding FAA Airworthiness Directive for additional context"],"plain_english_summary":"This CASA safety order targets Air Tractor AT‑300/400/500 series turbine aircraft (including piston‑to‑turbine conversions) after cracks were found in the vertical fin front spar fitting that could cause loss of control. Affected owners/operators must inspect per Snow Engineering Service Letter 155, ground the aircraft and replace the fitting if cracked, and install a steel doubler as a permanent fix within the mandated inspection and compliance timeframes to prevent catastrophic tail failure."}},"importantCases":[],"_links":{"self":"/api/acts/ad-at-25-vertical-fin-front-spar-fitting","history":"/api/acts/ad-at-25-vertical-fin-front-spar-fitting/history","analysis":"/api/acts/ad-at-25-vertical-fin-front-spar-fitting/analysis","conflicts":"/api/acts/ad-at-25-vertical-fin-front-spar-fitting/conflicts","importantCases":"/api/acts/ad-at-25-vertical-fin-front-spar-fitting/important-cases","documents":"/api/acts/ad-at-25-vertical-fin-front-spar-fitting/documents"}}