{"id":"F2006B09163","name":"AD/DHC-6/9 - Left and Right Hand Elevators Upper Skin - Modification","slug":"ad-dhc-6-9-left-and-right-hand-elevators-upper-skin-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":52892,"registerId":"commonwealth-F2006B09163-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DHC-6/9 - Left and Right Hand Elevators Upper Skin - 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)  DHC-6 (Twin Otter) Series Aeroplanes\n\n \n\nAD/DHC-6/9 Left and Right Hand Elevators Upper Skin - Modification\n\nApplicability: All models with S/Nos. 1 to 81.\n\n \n\nDocument:  De Havilland of Canada Mod. Bulletin 6/1142. Compliance: Before 1 April 1968.\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\n \n\n \n\n \n\n\n1/68\n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, single-issue airworthiness directive focused on a specific structural modification for early-model Twin Otter aircraft. It has not expanded beyond its original scope — it addresses exactly what it was issued for (elevator skin modification) with no subsequent amendments or extensions evident in this version."},"complexity_factors":["Extremely short document (approximately 150 words)","Only 2 defined applicability criteria (aircraft model and serial number range)","Single compliance requirement with clear deadline","No cross-references to other legislation beyond the enabling Civil Aviation Regulations 1998","No conditional logic or exceptions","References only one external technical document (Modification Bulletin 6/1142)"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** issued by Australia's Civil Aviation Safety Authority (CASA) under the Civil Aviation Regulations 1998. It mandates a specific safety modification for **De Havilland DHC-6 Twin Otter aircraft**.\n\n**What it requires:**\n- **Who must comply:** Owners or operators of DHC-6 Twin Otter aeroplanes with serial numbers 1 to 81 (the early production models)\n- **What must be done:** A modification to the **upper skin of both left and right elevators** (the movable control surfaces on the tail that make the plane pitch up and down)\n- **How to do it:** Follow the instructions in **De Havilland Modification Bulletin 6/1142**\n- **Deadline:** The work had to be completed **before 1 April 1968**\n\n**Why it matters:**\nAirworthiness Directives are legally binding safety orders. They are issued when a design flaw, manufacturing defect, or wear pattern is discovered that could affect flight safety. This particular AD addressed a structural issue with the elevator skins that, if left unmodified, could potentially compromise the aircraft's control or structural integrity.\n\n**Key point:** This is a **historical directive** — the compliance date of April 1968 has long passed. Any Twin Otter still flying today that falls within this serial number range would have had to complete this modification decades ago to remain airworthy."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The text specifies a clear, limited scope: modification of left and right elevator upper skin on DHC-6 aircraft serial numbers 1–81 per De Havilland Mod. Bulletin 6/1142, to be done before 1 April 1968. There is no indication in this document of any expansion, narrowing or later amendment to that scope."},"complexity_factors":["Narrow applicability (only DHC-6 aircraft with S/Ns 1–81) — reduces scope and stakeholder variety (Applicability).","Single, discrete mandated action tied to one manufacturer bulletin (De Havilland Mod. Bulletin 6/1142) — lowers procedural complexity but creates dependency on an external technical document (Document).","Fixed single compliance deadline (Before 1 April 1968) — simplifies regulatory timing but increases short-term scheduling pressure for affected operators (Compliance).","Technical execution requires maintenance capability and interpretation of the bulletin — introduces operational and technical complexity beyond the regulatory text (Document).","Regulatory enforcement is straightforward (a single AD issued by the Civil Aviation Safety Authority under Part 39) — low legal complexity but standard administrative oversight (header)."],"plain_english_summary":"AD/DHC-6/9 mandates a physical modification to the left and right elevator upper skins on De Havilland DHC‑6 (Twin Otter) aeroplanes with serial numbers 1–81, requiring work per De Havilland Mod. Bulletin 6/1142.  \n\nOwners/operators must complete the modification before 1 April 1968 under authority of the Civil Aviation Safety Authority; practical effects include compliance costs, aircraft downtime, and reliance on the manufacturer’s bulletin for technical execution."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-6-9-left-and-right-hand-elevators-upper-skin-modification","history":"/api/acts/ad-dhc-6-9-left-and-right-hand-elevators-upper-skin-modification/history","analysis":"/api/acts/ad-dhc-6-9-left-and-right-hand-elevators-upper-skin-modification/analysis","conflicts":"/api/acts/ad-dhc-6-9-left-and-right-hand-elevators-upper-skin-modification/conflicts","importantCases":"/api/acts/ad-dhc-6-9-left-and-right-hand-elevators-upper-skin-modification/important-cases","documents":"/api/acts/ad-dhc-6-9-left-and-right-hand-elevators-upper-skin-modification/documents"}}