{"id":"F2006B09132","name":"AD/DHC-6/43 Amdt 1 - Elevator Housing Assembly Lower Mounting Structure","slug":"ad-dhc-6-43-amdt-1-elevator-housing-assembly-lower-mounting-structure","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115685,"registerId":"commonwealth-F2006B09132-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DHC-6/43 Amdt 1 - Elevator Housing Assembly Lower Mounting Structure","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-6/43\n\nAmdt 1\n\n\nElevator Housing Assembly Lower Mounting Structure\n\n\n9/91\n\n \n\nApplicability: Model DHC-6 with serial numbers 2 through 494, 497 through 503, 505 and 507.\n\n \n\nRequirement: Action in accordance with the Technical Requirements of Transport Canada AD CF- 77-05 R1.\n\n \n\nNote: De Havilland SB 6/348 refers.\n\n \n\nCompliance: As specified in the Requirement Document.\n\n \n\nBackground: This amendment is raised to reflect transport Canada’s ageing aircraft program, which requires terminating action rather than repetitive inspections for known critical service problems.\n\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"The amendment changes the maintenance scope for the identified DHC-6 serial numbers by replacing repetitive inspections with a terminating action. The AD states this shift explicitly as being issued to reflect Transport Canada’s ageing aircraft program and to require terminating action rather than repetitive inspections for the identified critical service problem. (Background)"},"complexity_factors":["Relies on an external technical document (Transport Canada AD CF-77-05 R1) for all substantive steps and timing, requiring operators to obtain and interpret that document (Requirement, Compliance).","Serial-number-specific applicability requires operators to check aircraft identity before action (Applicability).","Change in maintenance regime from repetitive inspections to a terminating action shifts planning and cost profiles for operators (Background).","References a manufacturer service bulletin (De Havilland SB 6/348) as related material, adding an additional cross-reference to implementers (Note).","The AD text delegates technical specificity entirely to the Requirement Document, leaving the AD itself concise but dependent on external material for operational detail (Requirement, Compliance)."],"plain_english_summary":"This AD makes Transport Canada AD CF-77-05 R1 mandatory for certain De Havilland DHC-6 (Twin Otter) aeroplanes, requiring the terminating corrective action it prescribes rather than ongoing repetitive inspections. Operators of the affected aircraft must obtain and follow the Transport Canada document (and referenced De Havilland service material); they bear the costs and downtime, while CASA enforces compliance."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This amendment stays within the original scope of the airworthiness directive. It updates the compliance approach from repetitive inspections to terminating action, but this is a refinement of the existing safety measure rather than an expansion into new areas of regulation."},"complexity_factors":["Very short document (approximately 150 words)","Only 1 defined applicability criterion (specific serial number ranges)","Single requirement referencing an external technical document rather than spelling out detailed procedures","No nested exceptions or conditional logic","Minimal cross-referencing (only one referenced service bulletin and one Canadian AD)","Straightforward amendment purpose clearly stated in Background section"],"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) for specific aircraft.\n\n**What it does:** It requires owners and operators of certain De Havilland DHC-6 \"Twin Otter\" aeroplanes to fix a known safety problem with the **elevator housing assembly lower mounting structure** (a structural component that helps control the aircraft's pitch).\n\n**Who it affects:** Anyone who owns or operates DHC-6 Twin Otter aircraft with serial numbers 2 through 494, 497 through 503, 505 and 507.\n\n**What must be done:** Operators must follow the technical requirements set out in a Canadian aviation safety document (Transport Canada AD CF-77-05 R1). This amendment (Amendment 1) changes the previous approach: instead of repeatedly inspecting the problem over time, operators must now carry out **terminating action** — a permanent fix that resolves the issue once and for all.\n\n**Why it matters:** This addresses a **critical service problem** in an ageing aircraft fleet. The change from repetitive inspections to a permanent solution reduces long-term maintenance burden while ensuring continued airworthiness and passenger safety."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-6-43-amdt-1-elevator-housing-assembly-lower-mounting-structure","history":"/api/acts/ad-dhc-6-43-amdt-1-elevator-housing-assembly-lower-mounting-structure/history","analysis":"/api/acts/ad-dhc-6-43-amdt-1-elevator-housing-assembly-lower-mounting-structure/analysis","conflicts":"/api/acts/ad-dhc-6-43-amdt-1-elevator-housing-assembly-lower-mounting-structure/conflicts","importantCases":"/api/acts/ad-dhc-6-43-amdt-1-elevator-housing-assembly-lower-mounting-structure/important-cases","documents":"/api/acts/ad-dhc-6-43-amdt-1-elevator-housing-assembly-lower-mounting-structure/documents"}}