{"id":"F2006B09783","name":"AD/F28/49 - Wing Butt Straps and Boundary-Layer Fences","slug":"ad-f28-49-wing-butt-straps-and-boundary-layer-fences","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54702,"registerId":"commonwealth-F2006B09783-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F28/49 - Wing Butt Straps and Boundary-Layer Fences","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 F28 Series Aeroplanes\n\n \n\nAD/F28/49 Wing Butt Straps and Boundary-Layer Fences 9/85\n\nApplicability: All model F28 with S/Nos 11092, 11093, 11111 to 11203 and 11205 to 11231. Requirement:               Fokker SB F28/57-70.\n\nNote: Netherlands AD 85-44 refers.\n\n \n\nCompliance: Prior to 31 December 1985.\n\n \n\nAir-leakage through butt straps and boundary layer fences has an adverse effect on the aerodynamic behaviour of the wings.\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\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The instrument, as written, sets a clearly targeted requirement for specific Fokker F28 airframes to comply with Fokker SB F28/57-70 by a specified date. There is no language in the text indicating a change to the AD’s original scope; the applicability, required action, and compliance deadline are presented as the AD’s core scope and remain unchanged within this document (Applicability; Requirement; Compliance)."},"complexity_factors":["Narrow, specific applicability limited to enumerated serial numbers (reduces breadth but creates precise targeting)","Delegation of technical detail to an external Fokker Service Bulletin (implementers must obtain and follow another document)","Fixed compliance deadline creates scheduling pressure for affected operators","Cross-reference to a foreign AD (Netherlands AD 85-44) adds an external reference for background or corroboration","Directive text is short and leaves procedural and cost details to operators and the service bulletin (low legislative complexity but operational dependence)"],"plain_english_summary":"This directive obliges owners/operators of specified Fokker F28 airframes (listed serial numbers) to inspect and correct wing butt straps and boundary‑layer fences per Fokker Service Bulletin F28/57‑70, to be completed by 31 December 1985. It addresses air leakage that can impair wing aerodynamics; technical repair details and implementation choices are delegated to the referenced service bulletin and the operator/maintenance provider."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-limited airworthiness directive from 1985. It has not grown beyond its original purpose — it was always intended as a specific safety fix for a specific airframe issue, and the document reflects that narrow, technical scope."},"complexity_factors":["Extremely short document (under 200 words)","Only one substantive requirement referencing an external technical document (Fokker Service Bulletin)","No defined terms section — technical terms (butt straps, boundary-layer fences) are used without legal definitions","Simple conditional structure: applicability based on serial number list, single compliance deadline","No cross-references to other legislation beyond a note about a Netherlands AD","Single purpose: mandate one specific technical action by one specific date"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for specific aircraft.\n\n**What it does:**\nOrders owners and operators of certain **Fokker F28 series aeroplanes** to carry out a specific safety fix (detailed in \"Fokker Service Bulletin F28/57-70\") before the end of 1985.\n\n**Who it affects:**\nOwners and operators of Fokker F28 aircraft with specific serial numbers: 11092, 11093, 11111 through 11203, and 11205 through 11231.\n\n**Why it matters:**\nAir leaking through \"butt straps\" (metal joints connecting wing panels) and \"boundary-layer fences\" (small vertical fins on wings that control airflow) was messing up how air flows over the wings. Bad airflow = reduced lift, potential handling problems, and safety risks. This directive forces a fix before the problem could cause accidents.\n\n**Key point:** This is a **time-critical safety mandate** — compliance was legally required before 31 December 1985."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f28-49-wing-butt-straps-and-boundary-layer-fences","history":"/api/acts/ad-f28-49-wing-butt-straps-and-boundary-layer-fences/history","analysis":"/api/acts/ad-f28-49-wing-butt-straps-and-boundary-layer-fences/analysis","conflicts":"/api/acts/ad-f28-49-wing-butt-straps-and-boundary-layer-fences/conflicts","importantCases":"/api/acts/ad-f28-49-wing-butt-straps-and-boundary-layer-fences/important-cases","documents":"/api/acts/ad-f28-49-wing-butt-straps-and-boundary-layer-fences/documents"}}