{"id":"F2006B02204","name":"AD/AC-SNOW/13 - Horizontal Stabiliser Spar - Fatigue Inspection","slug":"ad-ac-snow-13-horizontal-stabiliser-spar-fatigue-inspection","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41434,"registerId":"commonwealth-F2006B02204-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AC-SNOW/13 - Horizontal Stabiliser Spar - Fatigue Inspection","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)  \nAyres Thrush (Snow) Commander Series Aeroplanes\n\nAD/AC-SNOW/13 Horizontal Stabiliser Spar \\- Fatigue Inspection\n\n  \n3/80\n\nApplicability: The following models and S/Nos. which have achieved 2000 hours or more total time in service and which incorporate horizontal stabiliser P/N 40221-61.\n\nModel S-2D: All S/Nos.;\n\nModel S-2R: S/Nos. 1416R thru 2560R; 5000R thru 5100R; Model S2R-T11: S/Nos. T11-001 and T11-002;\n\nModel S2R-T15: S/Nos. T15-001 thru T15-005;\n\nModel S2R-T34: S/Nos. 6000 thru 6049, T34-001 thru T34-019; Model S2R-R3S: S/Nos. R3S-001 thru R3S-008.\n\nRequirement: (a) Remove fuselage side skins to provide access to the inspection hole in the bottom of the horizontal stabiliser.\n\n    (b) Disconnect the flying wires, left and right sides, from both upper and lower surfaces of the horizontal stabiliser to permit the exercising of the stabiliser.\n\n    (c) Inspect the horizontal stabiliser front spar tube (P/N 40221 \\-19) in the area of both the left and right fuselage attach bushings as shown in Fig. 1 using a flashlight and an inspection mirror. IMPORTANT - the stabiliser must be exercised with both an up and down force at the tip during the inspection to ensure detection of crack.\n\nNote 1: The horizontal stabiliser assembly should be re-installed and the flying wires adjusted in accordance with the Rigging Procedures in Section VII of the Maintenance Manual, with the exception that the tension in each flying wire should be adjusted until the midpoint has a deflection of 0.30 + 0.05 inch with an applied side load of 20 pounds, rather than 35 pounds as stated in the Maintenance Manual.\n\nNote 2: FAA AD 80-04-06 Amdt. 39-3688 refers to this inspection.\n\nNote 3: Aircraft fitted with Horizontal stabiliser P/N 40221-70 are exempted from the requirements of this AD.\n\nCompliance: Within 25 hours’ time in service after 18 March 1980 and thereafter at intervals not exceeding 500 hours’ time in service.\n\nBackground: This AD is based purely on United States Federal Aviation Administration requirements. No other background information is available at this stage.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.002.png)  \n\nFIG 1.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive applies only to the listed Ayres Thrush (Snow) Commander serial numbers fitted with stabiliser P/N 40221-61 that have reached 2,000+ hours, with a clear exemption for P/N 40221-70. The text shows no amendment to the original applicability or scope and states it is based on the FAA AD, so scope has not been altered from the directive as presented."},"complexity_factors":["Model- and serial-number-specific applicability narrows the affected fleet and requires careful record checks","Operational requirement to remove fuselage side skins to gain access (maintenance labour and downtime)","Need to disconnect and later re-tension flying wires and re-rig the stabiliser (technical skill and reference to Maintenance Manual with a modified tension requirement)","Inspection technique requires exercising the stabiliser up and down while doing a visual inspection with flashlight and mirror to detect cracks (procedural specificity to find intermittent cracks)","Compliance timing: short initial compliance window (25 hours) followed by recurring 500‑hour intervals (scheduling burden)","Exemption for parts with different P/N (40221-70) creates an alternative-compliance pathway to track","Cross-reference to FAA AD (regulatory dependency and potential for differing foreign documentation)"],"plain_english_summary":"Requires owners/operators of specified Ayres Thrush (Snow) Commander aeroplanes fitted with horizontal stabiliser P/N 40221-61 and with 2,000+ hours to inspect the horizontal stabiliser front spar tube (P/N 40221-19) for fatigue cracks. Inspection requires removing fuselage side skins, disconnecting flying wires, exercising the stabiliser and visually inspecting with a flashlight and mirror. Compliance is within 25 hours after 18 March 1980 and then every 500 hours; aircraft with stabiliser P/N 40221-70 are exempt. The directive is based on a corresponding FAA AD."},"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 discrete, targeted safety directive focused on a specific structural fatigue issue in a narrow class of agricultural aircraft. The scope remains tightly bounded to the original safety purpose — preventing horizontal stabiliser failure through mandatory inspection. No evidence of scope creep or expansion beyond the original technical safety intent."},"complexity_factors":["Specific applicability matrix requiring cross-referencing of model, serial number ranges, and part numbers","Technical mechanical procedure with 3 distinct steps requiring specialised aviation maintenance knowledge","Precise measurement specification in Note 1 (0.30 + 0.05 inch deflection with 20 pounds load, overriding the 35 pounds in the manual)","Conditional exemption clause (Note 3) based on alternative part number","Compliance deadline calculated from a fixed historical date (18 March 1980) plus flight hours, creating a rolling obligation","Reference to external FAA directive (80-04-06 Amdt. 39-3688) for context"],"plain_english_summary":"This CASA Airworthiness Directive mandates repeated physical inspections of the horizontal stabiliser spar on certain Ayres Thrush (Snow) Commander agricultural aircraft (specific models/serials with P/N 40221‑61 and >2,000 hours). Inspectors must exercise the tail during checks and repeat them every 500 flight hours. It addresses metal fatigue that could cause catastrophic tail failure in hard‑working crop dusters. Aircraft fitted with the newer P/N 40221‑70 stabiliser are exempt."}},"importantCases":[],"_links":{"self":"/api/acts/ad-ac-snow-13-horizontal-stabiliser-spar-fatigue-inspection","history":"/api/acts/ad-ac-snow-13-horizontal-stabiliser-spar-fatigue-inspection/history","analysis":"/api/acts/ad-ac-snow-13-horizontal-stabiliser-spar-fatigue-inspection/analysis","conflicts":"/api/acts/ad-ac-snow-13-horizontal-stabiliser-spar-fatigue-inspection/conflicts","importantCases":"/api/acts/ad-ac-snow-13-horizontal-stabiliser-spar-fatigue-inspection/important-cases","documents":"/api/acts/ad-ac-snow-13-horizontal-stabiliser-spar-fatigue-inspection/documents"}}