{"id":"F2006B08414","name":"AD/CESSNA 550/1 - Wing Main Spar - Inspection and Modification","slug":"ad-cessna-550-1-wing-main-spar-inspection-and-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115878,"registerId":"commonwealth-F2006B08414-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CESSNA 550/1 - Wing Main Spar - Inspection and Modification","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-generator: Aspose.Words for .NET 22.10.0\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)  Cessna 550 (Citation II) Series Aeroplanes\n\n \n\n# AD/CESSNA 550/1 Wing Main Spar - Inspection and Modification\n\nApplicability: Model 550 series aeroplanes with S/Nos. as referenced in SL No. 550-57-1. Requirement:               1. Inspect the wing spar upper and lower cap in the area of wing station 37 in\n\n# 2/82\n\naccordance with Cessna SL No. 550-57-1 Rev. 1 dated 1 May 1979. FAA AD 79-12-06 also refers.\n\n2.    Inspect and modify in accordance with Cessna SB No. 550-57-3 Rev. 1 dated 28 March 1980.\n\n \n\n3.    Visually inspect for further cracks the wing main spar upper and lower caps of aircraft modified in accordance with SB No. 550-57-3 Rev. 1 in the area of the WS 37 modification.\n\n \n\nCompliance: For Para. 1 - As detailed in the requirement document.\n\n \n\nFor Para. 2 - In accordance with the requirement document when any crack monitored under the provisions of Para. 1 reaches or exceeds 0.30 inches in length.\n\n \n\nNote: The modification may be carried out at any time (i.e. not necessarily at crack detection) and thus exempt the aircraft from the inspections under Para. 1.\n\n \n\nFor Para. 3 - At or prior to exceeding 1200 hours after modification and thereafter at intervals not exceeding 1200 hours or 1200 landings whichever occurs first.\n\n \n\nBackground:  The results of full-scale fatigue testing and the inspection of several high time Citation aircraft have revealed small fatigue cracks in the main spar upper and lower caps at WS 37. In service cracks were found in 8 instances in the upper cap and in 1 instance in the lower cap.\n\n \n\n \n\n \n\n \n\n \n\n \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":{"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"},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"The directive’s scope is consistent with its stated aim in the background: to detect and mitigate fatigue cracks in the main spar at WS 37 on specified Cessna 550 aircraft. It applies only to serial numbers referenced in the manufacturer’s service letter and prescribes inspection thresholds, a modification option that can eliminate initial inspections, and recurring inspections after modification (Requirement Paras. 1–3; Compliance)."},"complexity_factors":["Technical inspection threshold (crack length ≥ 0.30 inches) adds measurable judgment to detection and acceptance criteria (Compliance Para. 2).","Applicability tied to serial numbers listed in an external Cessna service letter (SL No. 550-57-1) requires cross-referencing documents to identify affected aircraft (Applicability).","Mandatory modification is specified by a separate service bulletin (SB No. 550-57-3 Rev. 1), creating dependency on manufacturer instructions and parts availability (Requirement Para. 2).","Optional timing: modification may be carried out at any time to exempt the aircraft from initial inspections, creating a strategic decision for operators (Note under Compliance Para. 2).","Recurring inspection interval after modification (every 1,200 hours or 1,200 landings) imposes ongoing compliance scheduling and record-keeping (Requirement Para. 3).","Reference to FAA AD 79-12-06 introduces regulatory cross-jurisdictional coordination and potential alignment of obligations (Requirement Para. 1).","Operational impact: inspections, modifications and associated downtime and costs fall on owners/operators and their maintenance providers, affecting availability and budgeting (Compliance overall)."],"plain_english_summary":"This airworthiness directive requires owners/operators of certain Cessna 550 (Citation II) aeroplanes (serial numbers listed in the cited Cessna service letter) to inspect the wing main spar at wing station 37 for fatigue cracks and, if a crack reaches 0.30 inches, to carry out a prescribed modification. After modification, the spar must be visually checked at intervals not exceeding 1,200 hours or 1,200 landings. Owners/operators and their maintenance organisations must schedule, perform and pay for the inspections and any modification per the referenced Cessna documents."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a focused, original airworthiness directive addressing a specific structural fatigue issue identified through testing and in-service findings. The scope remains tightly limited to wing spar inspections and modifications for the affected Cessna 550 series aircraft."},"complexity_factors":["Short, single-purpose directive with only 3 numbered requirements","Minimal defined terms (relies on external Cessna documents for technical specifications)","Simple conditional logic: 'if crack ≥ 0.30 inches, then modify'","Straightforward compliance schedule with clear time intervals (1200 hours/landings)","Single cross-reference to FAA AD 79-12-06 for additional context","No nested exceptions or complex definitional sections"],"plain_english_summary":"This CASA Airworthiness Directive mandates inspections and corrective action for the wing main spar caps near wing station 37 on certain Cessna 550 Citation II jets (serials listed in Cessna Service Letter 550-57-1). Owners/operators must inspect for fatigue cracks, modify if cracks reach 0.30\" (or elect to modify proactively), and if modified perform recurrent visual checks every 1,200 flight hours or landings.\n\nIt matters because discovered fatigue cracks in this high‑stress area could lead to catastrophic wing‑spar failure if not caught and fixed."}},"importantCases":[],"_links":{"self":"/api/acts/ad-cessna-550-1-wing-main-spar-inspection-and-modification","history":"/api/acts/ad-cessna-550-1-wing-main-spar-inspection-and-modification/history","analysis":"/api/acts/ad-cessna-550-1-wing-main-spar-inspection-and-modification/analysis","conflicts":"/api/acts/ad-cessna-550-1-wing-main-spar-inspection-and-modification/conflicts","importantCases":"/api/acts/ad-cessna-550-1-wing-main-spar-inspection-and-modification/important-cases","documents":"/api/acts/ad-cessna-550-1-wing-main-spar-inspection-and-modification/documents"}}