{"id":"F2006B02206","name":"AD/AC-SNOW/15 - Forward Fuselage Upper Longerons - Inspection and Modification","slug":"ad-ac-snow-15-forward-fuselage-upper-longerons-inspection-and-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41436,"registerId":"commonwealth-F2006B02206-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AC-SNOW/15 - Forward Fuselage Upper Longerons - Inspection and Modification","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-description: CASA Airworthiness Directive\nmeta-generator: Aspose.Words for .NET 22.10.0\nmeta-keywords: Issue 6/1984,Aircraft below 5700 kg,Ayres Thrush (Snow) Commander Series Aeroplanes,Forward Fuselage Upper Longerons - Inspection and Modification,15\ntitle: Airworthiness Directive - AD/AC-SNOW/15 - Forward Fuselage Upper Longerons - Inspection and Modification\n---\n\n?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"no\"?>\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  Ayres Thrush (Snow) Commander Series Aeroplanes\n\n \n\n# AD/AC-SNOW/15  Forward Fuselage Upper Longerons - Inspection and Modification\n\nApplicability: All models S2R-R1820 with S/Nos R1820-001 to R1820-031.\n\n# 6/84\n\n \n\nRequirement: 1. Visually inspect the forward fuselage upper longerons for Cracks in accordance with the following:\n\n \n\n(a)     remove the fuselage side skins located between the wing upper surface and the hopper to gain access to the upper longerons between the firewall and the cockpit.\n\n \n\n(b)     check the longerons in the areas shown in Fig 1 of Ayres Corporation SB No SB-AG-16 dated 1 April 1984 as follows:\n\n \n\n(i)       between the upper engine mount and first hopper attachment bracket;\n\n \n\n(ii)     each vertical and diagonal tube intersection at the upper longeron;\n\n \n\n(iii)  each hopper attachment bracket.\n\n \n\n2. Incorporate tubular split-sleeve modification P/N CK-AG-19 on both upper longerons in accordance with Ayres Corporation SB No SB-AG-16.\n\n \n\nNote: FAA Ayres Emergency AD dated 7 May 1984 refers.\n\n \n\nCompliance: For para 1: Before further flight after 17 May 1984 and thereafter at intervals not exceeding 10 hours’ time in service, until modified in accordance with para 2.\n\n \n\nNote: This inspection may be accomplished by the pilot in command in which case the pilot shall enter and certify for this AD in column 2 part 3 of the maintenance release on each occasion.\n\n \n\nFor para 2: Within 100 hours’ time in service after 17 May 1984.\n\n \n\nBackground: Failure of both upper longerons has occurred on aircraft in service overseas. This condition if undetected could result in separation of the engine in flight.\n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope — addressing a specific structural failure risk in a limited production run of agricultural aircraft. It has not expanded beyond its original safety purpose."},"complexity_factors":["Single, specific aircraft type and serial number range (narrow applicability)","Only two main requirements: visual inspection and physical modification","Clear, sequential numbering (1(a), 1(b)(i)-(iii), 2)","Simple compliance timeline with two distinct deadlines","One defined technical reference (Ayres Corporation SB No SB-AG-16)","Minimal cross-referencing (only one FAA Emergency AD mentioned in a note)","No nested exceptions or conditional logic — requirements apply uniformly to all affected aircraft"],"plain_english_summary":"This CASA safety order requires urgent, repeated inspections and a permanent reinforcement for the forward-fuselage longerons on Ayres Thrush (Snow) Commander aircraft serial R1820-001 to R1820-031. Cracked longerons have led to engines separating in flight, so owners/operators must have the beams sleeved by a licensed mechanic within 100 flight hours. Pilots may perform and log the visual checks before flying and every 10 flight hours until the fix."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The AD remains focused on a single, safety‑driven purpose: detect and fix cracking of the forward fuselage upper longerons on a narrowly defined set of Ayres Thrush S2R‑R1820 aeroplanes. It does not expand regulatory reach beyond that technical safety objective. The instrument prescribes temporary mitigation (frequent inspections) followed by a mandated structural modification; this stays within the original intent of addressing the reported overseas failures and preventing engine separation."},"complexity_factors":["Short instrument (one page) with limited parts","Single, narrow applicability (specific model and serial numbers)","Few defined terms (no extensive interpretation section)","Two main obligations only: recurring visual inspections and a single modification","Conditional logic: repeated inspections until modification is fitted (simple conditional)","Cross‑references to one manufacturer Service Bulletin (SB‑AG‑16), a part number (CK‑AG‑19), and an FAA Emergency AD (adds external dependency)","Certification option allowing pilot to sign maintenance release (adds a small procedural hook)"],"plain_english_summary":"**What this instrument does (mechanically)**\n\n- It requires owners/operators of Ayres Thrush (Snow) Commander S2R‑R1820 aeroplanes with serial numbers R1820‑001 to R1820‑031 to inspect and then modify the forward fuselage upper longerons (the upper longitudinal structural tubes of the forward fuselage).\n\n- Inspection: Remove the fuselage side skins between the wing upper surface and the hopper to gain access, and visually inspect the upper longerons in the specific areas shown in Ayres Service Bulletin SB‑AG‑16 (dated 1 April 1984):\n  - between the upper engine mount and the first hopper attachment bracket;\n  - at each vertical and diagonal tube intersection with the upper longeron;\n  - at each hopper attachment bracket. (See AD Requirement para 1(a)–(b) and (i)–(iii).)\n\n- Frequency before modification: Perform this visual inspection before the next flight after 17 May 1984 and then every 10 hours time‑in‑service until the modification is fitted. The AD explicitly permits the pilot‑in‑command to perform and certify this inspection in the aircraft’s maintenance release (AD Compliance paragraph for para 1 and Note). \n\n- Modification: Install the tubular split‑sleeve modification, part number CK‑AG‑19, on both upper longerons in accordance with Ayres SB‑AG‑16. The modification must be completed within 100 hours time‑in‑service after 17 May 1984 (AD Requirement para 2; Compliance for para 2).\n\n- Safety rationale stated in the AD: Failures of both upper longerons have occurred overseas; undetected failure could allow separation of the engine in flight (Background). The AD cross‑refers an FAA Ayres Emergency AD of 7 May 1984.\n\n**Who this affects**\n\n- Aircraft owners and operators of the specified Ayres Thrush S2R‑R1820 serial numbers.\n- Pilots who may be authorised to perform and certify the repeated visual inspections.\n- Maintenance organisations or engineers who will perform the modification and any inspections requiring skin removal.\n\n**Why it matters (practical effect)**\n\n- It imposes an immediate safety inspection regime (frequent 10‑hour checks) and a mandatory structural modification within a fixed deadline (100 hours) to reduce the risk of catastrophic structural failure of the forward fuselage and possible engine separation.\n\n**Implementation mechanics and practical implications**\n\n- Who pays: owners/operators bear direct costs — labour to remove skins and inspect, parts for the split‑sleeve (P/N CK‑AG‑19), and labour/time to fit the modification.\n\n- Who decides/acts: operators decide scheduling; the maintenance organisation or the pilot (for the visual inspections) actually conducts the checks. The AD requires the pilot to record and certify inspections in the maintenance release when the pilot acts as inspector (AD Note).\n\n- Behaviour changes required: frequent interim inspections until modification is fitted; scheduling the aircraft offline to have the modification installed within the 100‑hour deadline; possible temporary grounding if cracks are found.\n\n**Costs, risks and trade‑offs**\n\n- Compliance cost: repeated inspections every 10 hours impose recurring time and operational disruption until the modification is fitted. The modification has one‑off parts and installation cost and some downtime.\n\n- Inspection effectiveness and implementation risk: the inspections required are visual and may miss subsurface or small cracks. Allowing the pilot to perform inspections lowers certified maintenance costs but transfers detection responsibility to the operator/pilot and may increase risk of missed defects if the inspector lacks training or access to required inspection views.\n\n- Opportunity cost: hours spent on inspections and modification are hours the aircraft cannot be used for revenue flights (relevant for agricultural or charter operators using these types).\n\n- Enforcement and discretion: compliance is a regulatory requirement enforced by the civil aviation authority; the AD refers to Ayres SB‑AG‑16 for exact inspection locations and modification detail, so execution depends on the content of that Service Bulletin.\n\n**Effect on private enterprise and market factors**\n\n- Competition/ownership: the AD does not alter ownership or market entry rules. It raises operating costs for affected owners/operators, which may disadvantage operators with multiple affected airframes or small operators with limited maintenance resources.\n\n- Prices and productivity: the need for repeated inspections and a mandatory modification will reduce aircraft availability and raise operating costs per flight hour until the modification is fitted, reducing productivity for operators who rely on these aircraft.\n\n- Contract freedom and business choices: operators must comply with the AD; they can choose how to schedule the inspections and modification (e.g., when to ground the aircraft), but they cannot lawfully continue flying beyond inspection requirements or the 100‑hour modification deadline without complying.\n\n**Cross‑references and documentation relied on**\n\n- The AD requires inspection and modification procedures “in accordance with” Ayres Service Bulletin SB‑AG‑16 (1 April 1984) and specifies modification P/N CK‑AG‑19. It also refers to the FAA Ayres Emergency AD dated 7 May 1984.\n\n**Concrete timelines from the AD**\n\n- First inspection: before further flight after 17 May 1984; repeat every 10 hours until modification fitted (Compliance for para 1).\n- Modification deadline: within 100 hours time‑in‑service after 17 May 1984 (Compliance for para 2).\n\n(References in summary: AD Requirement paras 1–2; Compliance paragraphs; Note permitting pilot inspection; Background.)"},"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"}},"importantCases":[],"_links":{"self":"/api/acts/ad-ac-snow-15-forward-fuselage-upper-longerons-inspection-and-modification","history":"/api/acts/ad-ac-snow-15-forward-fuselage-upper-longerons-inspection-and-modification/history","analysis":"/api/acts/ad-ac-snow-15-forward-fuselage-upper-longerons-inspection-and-modification/analysis","conflicts":"/api/acts/ad-ac-snow-15-forward-fuselage-upper-longerons-inspection-and-modification/conflicts","importantCases":"/api/acts/ad-ac-snow-15-forward-fuselage-upper-longerons-inspection-and-modification/important-cases","documents":"/api/acts/ad-ac-snow-15-forward-fuselage-upper-longerons-inspection-and-modification/documents"}}