{"id":"F2006B08437","name":"AD/CESSNA 550/9 - Airframe Ice Protection System Proportioning Units","slug":"ad-cessna-550-9-airframe-ice-protection-system-proportioning-units","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115926,"registerId":"commonwealth-F2006B08437-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CESSNA 550/9 - Airframe Ice Protection System Proportioning Units","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 550/9 Airframe Ice Protection System\n\nProportioning Units\n\nApplicability: All model S550 with unit numbers -0001 to -0075.\n\n# 2/86\n\n \n\nRequirement: 1. Install the following placard on the instrument panel in full view of the pilot using letters of at least 5mm in height: “Flight into Known or Forecast Icing Prohibited”.\n\n \n\n2. Perform the requirements of FAA AD 85-24-04 paragraphs B.1, 2, 3 and 4.\n\n \n\nCompliance: 1. Prior to further flight after 20 December 1985 until the actions of paragraph 2 of the Requirement have been complied with.\n\n \n\n2. Within 100 hours time in service after 28 February 1986.\n\n \n\nBackground:  The manufacturer has identified a production error resulting in incorrect installation of fluid ice protection system proportioning units. This Directive removes approval for flight into icing conditions and requires inspection and replacement, as necessary, of the fluid protection system proportioning units.\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\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":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"The Directive removes approval for flight into known or forecast icing for the affected S550 serials until inspections/replacements are completed (see Requirement 1 and Background) and mandates compliance with FAA AD 85-24-04 (Requirement 2). Applicability is limited to units -0001 to -0075; compliance timing is immediate for the placard and within 100 hours of service for the inspections/replacements (see Compliance)."},"complexity_factors":["Narrow applicability by specific unit/serial numbers (-0001 to -0075)","Cross-reference dependency on FAA AD 85-24-04 for technical inspection and corrective steps","Two-tier compliance timing: immediate placard requirement plus a 100‑hour inspection/replacement deadline","Technical work (inspection/replacement) requires certified maintenance action and parts availability","Operational effect (temporary prohibition on flight into icing) that may ground aircraft until compliance is demonstrated"],"plain_english_summary":"Requires owners/operators of Cessna 550 (S550) aeroplanes with unit numbers -0001 to -0075 to fit a 5 mm‑letter placard forbidding flight into known or forecast icing immediately, and to perform inspection and any necessary replacement of the fluid ice‑protection system proportioning units in accordance with FAA AD 85‑24‑04 within 100 hours. The Directive withdraws approval for flight into icing for the affected serials until the corrective actions are complete."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific manufacturing defect in a limited aircraft population. The scope remains precisely focused on the identified ice protection system issue without expansion into broader operational or maintenance requirements."},"complexity_factors":["Very short document (approximately 250 words)","Only 2 substantive requirements with clear deadlines","Single cross-reference to external FAA directive (AD 85-24-04)","No defined terms section — common aviation terminology used","Simple conditional logic: temporary restriction → permanent repair","Narrow applicability (specific model and serial number range)"],"plain_english_summary":"This AD applies to early Cessna 550 Citation II (S550 serials -0001 to -0075) that may have had ice-protection proportioning units installed incorrectly. It requires grounding from known/forecast icing (via an instrument‑panel placard) until the FAA-mandated inspection/repair is done to correct the fluid-flow units. It matters because faulty de-icing hardware can allow dangerous ice buildup, degrading control and risking loss of the aircraft."}},"importantCases":[],"_links":{"self":"/api/acts/ad-cessna-550-9-airframe-ice-protection-system-proportioning-units","history":"/api/acts/ad-cessna-550-9-airframe-ice-protection-system-proportioning-units/history","analysis":"/api/acts/ad-cessna-550-9-airframe-ice-protection-system-proportioning-units/analysis","conflicts":"/api/acts/ad-cessna-550-9-airframe-ice-protection-system-proportioning-units/conflicts","importantCases":"/api/acts/ad-cessna-550-9-airframe-ice-protection-system-proportioning-units/important-cases","documents":"/api/acts/ad-cessna-550-9-airframe-ice-protection-system-proportioning-units/documents"}}