{"id":"F2006B09146","name":"AD/DHC-6/58 - Wing Struts Internal Beam Corrosion","slug":"ad-dhc-6-58-wing-struts-internal-beam-corrosion","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115710,"registerId":"commonwealth-F2006B09146-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DHC-6/58 - Wing Struts Internal Beam Corrosion","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 9/1985,Aircraft below 5700 kg,DHC-6 (Twin Otter) Series Aeroplanes,Wing Struts Internal Beam Corrosion,58\ntitle: Airworthiness Directive - AD/DHC-6/58 - Wing Struts Internal Beam Corrosion\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)  DHC-6 (Twin Otter) Series Aeroplanes\n\n \n\nAD/DHC-6/58 Wing Struts Internal Beam Corrosion 9/85\n\nApplicability: All models.\n\n \n\nRequirement: Action in accordance with De Havilland Aircraft of Canada Service Bulletin No.\n\n6/474.\n\n \n\nCompliance: As per “Requirement” Document.\n\n \n\nBackground: The manufacturer reports two struts on the same aircraft displaying exfoliation corrosion in the strut beam flanges enclosed by the strut skins.\n\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The instrument requires operators of all DHC-6 models to carry out the actions set out in De Havilland Service Bulletin No. 6/474 to address reported corrosion in wing strut internal beam flanges. The AD text confines itself to mandating compliance with that Service Bulletin and cites the manufacturer’s report of exfoliation corrosion as the reason; it does not expand or narrow that stated purpose within the text provided."},"complexity_factors":["Directive text is short and procedural: it mandates compliance with an external Service Bulletin rather than prescribing technical detail.","Dependence on Service Bulletin No. 6/474 for all inspection/repair specifics requires access to and interpretation of an external technical document.","Applicability to 'All models' widens operational scope and affects all operators of the type.","No compliance timeframe or intervals are specified in the AD text, creating potential ambiguity about timing and enforcement.","Technical subject matter (internal beam corrosion) requires specialist maintenance skills, parts and diagnostic access, increasing practical complexity for operators."],"plain_english_summary":"The directive requires all De Havilland DHC‑6 (Twin Otter) operators to carry out the inspections/repairs set out in De Havilland Service Bulletin No. 6/474, after the manufacturer reported exfoliation corrosion in internal strut beam flanges. It affects aircraft owners/operators and the maintenance organisations that perform the work, shifting cost, downtime and compliance responsibility to operators while relying on the Service Bulletin for technical detail."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive focused solely on a specific corrosion issue in DHC-6 wing struts. It has not expanded beyond its original purpose; it remains a narrow technical maintenance requirement."},"complexity_factors":["Extremely short document (under 200 words)","Only 1 defined term implicitly referenced (Service Bulletin 6/474 — external document)","No conditional logic or nested exceptions","Single, unambiguous requirement: comply with external manufacturer bulletin","No cross-references to other legislation beyond basic enabling authority (Civil Aviation Regulations 1998, Part 39)","Flat structure: Applicability → Requirement → Compliance → Background"],"plain_english_summary":"**What this is:** This is an **Airworthiness Directive (AD)** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). Think of it as a \"recall notice\" for aircraft, but legally binding.\n\n**What it does:** It requires owners and operators of **De Havilland DHC-6 Twin Otter aircraft** (all models) to inspect and fix a specific corrosion problem in the wing struts.\n\n**The safety issue:** The manufacturer found **exfoliation corrosion** (a type of rust that flakes and spreads between metal layers) in the internal beams of the wing struts — the structural supports that hold the wings to the fuselage. Two struts on the same aircraft showed this damage. This is serious because wing struts carry massive flight loads; if they fail, the wing could detach.\n\n**What must be done:** Operators must follow **De Havilland Service Bulletin 6/474** — a technical instruction from the manufacturer detailing exactly how to inspect for this corrosion and what repairs or replacements are needed.\n\n**Who it affects:** Anyone who owns, operates, or maintains DHC-6 Twin Otter aircraft in Australia.\n\n**Why it matters:** Corrosion in critical structural components can lead to catastrophic failure. This AD ensures the problem is caught and fixed before it causes an accident."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-6-58-wing-struts-internal-beam-corrosion","history":"/api/acts/ad-dhc-6-58-wing-struts-internal-beam-corrosion/history","analysis":"/api/acts/ad-dhc-6-58-wing-struts-internal-beam-corrosion/analysis","conflicts":"/api/acts/ad-dhc-6-58-wing-struts-internal-beam-corrosion/conflicts","importantCases":"/api/acts/ad-dhc-6-58-wing-struts-internal-beam-corrosion/important-cases","documents":"/api/acts/ad-dhc-6-58-wing-struts-internal-beam-corrosion/documents"}}