{"id":"F2006B09854","name":"AD/F50/28 - Stringer 18 Between Stations 4875 and 5325","slug":"ad-f50-28-stringer-18-between-stations-4875-and-5325","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54928,"registerId":"commonwealth-F2006B09854-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F50/28 - Stringer 18 Between Stations 4875 and 5325","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)  Fokker F50 (F27 Mk 50) Series Aeroplanes\n\n \n\nAD/F50/28 Stringer 18 Between Stations 4875 and 5325 13/89\n\nApplicability: F27 Mark 50 aircraft serial numbers 20103 through 20108 and 20110 through 20123. Requirement:               Action in accordance with Fokker Service Bulletin F50-53-017, dated 30 June 1989.\n\nNote: RLD BLA 89-077 dated 12 July 1989 refers.\n\n \n\nCompliance: Prior to accumulating 10000 flights.\n\n \n\nBackground: During full-scale fatigue testing, cracks were found in the skin, near the intercostal of the toilet wash-water tank. These cracks were found to initiate at the dimpled rivet holes in the skin-to-stringer connection. To improve the fatigue life of this connection, inspection and reinforcement of the affected skin is required.\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\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 is a discrete, targeted safety directive addressing a specific structural defect identified during fatigue testing. It has not expanded beyond its original purpose of mandating inspection and repair of a known cracking issue in a defined aircraft population."},"complexity_factors":["Single, specific applicability criterion (serial number ranges)","Single mandatory action referencing an external technical document (Fokker Service Bulletin)","Simple compliance deadline (flight hours/cycles threshold)","No defined terms section","No cross-references to other legislation or regulations","Straightforward background explanation without conditional logic"],"plain_english_summary":"This CASA Airworthiness Directive requires owners/operators of specific Fokker F50s (serials 20103–20108, 20110–20123) to inspect and reinforce fuselage Stringer 18 between Stations 4875 and 5325. Fatigue testing found rivet‑hole cracks near the toilet wash‑water tank that could lead to structural failure or decompression. Compliance with Fokker Service Bulletin F50‑53‑017 is mandated before 10,000 flights."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"Scope is confined to the listed F27 Mark 50 serial numbers and the specific skin-to-stringer area identified; it addresses fatigue cracking discovered in testing and does not expand obligations to other models or areas beyond those specified in the directive and referenced service bulletin."},"complexity_factors":["Narrow applicability to a defined set of serial numbers (Applicability).","Mandates technical work ‘in accordance with’ an external manufacturer service bulletin (Requirement), creating dependency on that document for procedural detail.","Clear compliance trigger tied to flight cycles: action required before 10,000 flights (Compliance), which requires operators to track cycles and schedule maintenance.","Work type is inspection plus structural reinforcement (Background: inspection and reinforcement required), requiring certified maintenance capability and possible part availability.","Low regulatory discretion: AD prescribes the service-bulletin method rather than leaving method choice to operators, reducing interpretive complexity but increasing operational coordination."],"plain_english_summary":"This airworthiness directive requires specified Fokker F27 Mark 50 aeroplanes (serial numbers 20103–20108 and 20110–20123) to be inspected and reinforced at the skin-to-stringer connection in the area between stations 4875 and 5325, following Fokker Service Bulletin F50‑53‑017. Compliance must be completed before the aircraft accumulates 10,000 flights. \n\nThe measure responds to fatigue cracks found during testing near the toilet wash‑water tank. Compliance costs and scheduling fall to affected operators; the service bulletin supplies the technical steps."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f50-28-stringer-18-between-stations-4875-and-5325","history":"/api/acts/ad-f50-28-stringer-18-between-stations-4875-and-5325/history","analysis":"/api/acts/ad-f50-28-stringer-18-between-stations-4875-and-5325/analysis","conflicts":"/api/acts/ad-f50-28-stringer-18-between-stations-4875-and-5325/conflicts","importantCases":"/api/acts/ad-f50-28-stringer-18-between-stations-4875-and-5325/important-cases","documents":"/api/acts/ad-f50-28-stringer-18-between-stations-4875-and-5325/documents"}}