{"id":"F2006B09099","name":"AD/DHC-6/12 - Aileron Mass Balance - Modification","slug":"ad-dhc-6-12-aileron-mass-balance-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115652,"registerId":"commonwealth-F2006B09099-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DHC-6/12 - Aileron Mass Balance - 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-6/12 Aileron Mass Balance - Modification 6/68\n\nApplicability: All models with S/Nos. 1 to 115.\n\n \n\nDocument:  De Havilland Aircraft of Canada Mod. Bulletin No. 6/1104. Compliance: Before 1 September 1968.\n\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive from 1968. It has not expanded beyond its original narrow purpose of correcting a specific aileron mass balance defect in early DHC-6 aircraft. The document appears to be a historical record preserved in the Schedule of Airworthiness Directives."},"complexity_factors":["Extremely short document (under 150 words)","Only 4 operative elements: applicability, reference document, required action, and deadline","No defined terms section — uses standard aviation terminology only","No cross-references to other legislation beyond the parent Civil Aviation Regulations 1998","No conditional logic or exceptions — applies to all listed serial numbers without qualification","Single compliance pathway (one specific modification bulletin)"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for aircraft.\n\n**What it does:**\n- Requires owners/operators of specific De Havilland DHC-6 Twin Otter aircraft to modify the **aileron mass balance** (a weight system that prevents dangerous vibrations in the wing control surfaces)\n- The modification must follow De Havilland's official technical bulletin (Mod. Bulletin No. 6/1104)\n\n**Who it affects:**\n- All DHC-6 Twin Otter aircraft with **serial numbers 1 through 115** (early production models)\n\n**Why it matters:**\n- Aileron flutter (uncontrolled vibration) can cause catastrophic structural failure and loss of control\n- This AD addresses a known safety defect in early Twin Otters before a fatal incident occurs\n- **Compliance deadline:** Before 1 September 1968 — meaning this is a historical directive that has long since passed\n\n**Key point:** This is not new law. It's a **historical aviation safety order** from 1968 that was archived in Australia's aviation regulations. Modern aircraft in this serial range would have complied decades ago or been retired."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The source provides a single, narrowly targeted directive: require the aileron mass-balance modification for DHC-6 aircraft S/N 1–115 to be completed by 1 September 1968. The extract contains no indication that the scope of affected aircraft or the nature of the required work was altered from an earlier or original intent; it sets out the applicability, the referenced manufacturer document, and the compliance date without showing a change in scope."},"complexity_factors":["Narrow, specific applicability (only DHC-6 S/N 1–115). (Applicability)","Single, well-defined required action (aileron mass-balance modification) referenced to a single manufacturer's bulletin. (Document)","Clear fixed compliance deadline (before 1 September 1968). (Compliance)","Lack of procedural detail in the AD text itself — technical steps and implementation details are contained in an external modification bulletin, requiring access to that document. (Document)","No information in the extract on cost allocation, alternative compliance or exemption procedures, creating practical uncertainty for operators about funding and approvals. (Document)"],"plain_english_summary":"This Airworthiness Directive mandates installation of the aileron mass‑balance modification on De Havilland DHC‑6 (Twin Otter) aeroplanes serial numbers 1–115, carried out per De Havilland Modification Bulletin No. 6/1104 and completed by 1 September 1968. It is a mandatory Commonwealth/CASA requirement; the extract gives the action and deadline but does not state the safety rationale, costs, or alternative‑compliance options."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-6-12-aileron-mass-balance-modification","history":"/api/acts/ad-dhc-6-12-aileron-mass-balance-modification/history","analysis":"/api/acts/ad-dhc-6-12-aileron-mass-balance-modification/analysis","conflicts":"/api/acts/ad-dhc-6-12-aileron-mass-balance-modification/conflicts","importantCases":"/api/acts/ad-dhc-6-12-aileron-mass-balance-modification/important-cases","documents":"/api/acts/ad-dhc-6-12-aileron-mass-balance-modification/documents"}}