{"id":"F2006L02519","name":"AD/DHC-6/74 - State of Design Airworthiness Directives","slug":"ad-dhc-6-74-state-of-design-airworthiness-directives","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":59744,"registerId":"commonwealth-F2006L02519-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"DHC-6 (Twin Otter) Series Aeroplanes","sectionType":"division","heading":"DHC-6 (Twin Otter) Series Aeroplanes","content":"### DHC-6 (Twin Otter) Series Aeroplanes\n\n| AD/DHC-6/74 | State of Design Airworthiness Directives | 9/2006 |\n| ----------- | ---------------------------------------- | ------ |\n\n```html\n

Applicability:

DHC-6 series aeroplanes.

Requirement:

1. Determine the applicability of the Transport Canada Airworthiness Directives (AD) listed in Table 1.

2. If it is determined that a Transport Canada AD is applicable and has not been previously accomplished, perform the actions required by that AD.

Table 1

Transport Canada AD

Effective Date

Title

CF-70-10

15 January 1971

Circuit Wires

CF-71-12

30 November 1971

AC Power

CF-73-04

18 June 1973

Prop Auto-Feather System

CF-73-09

29 June 1973

Auto-Feather System

CF-75-11

1 December 1975

Reverse Current Relays - Hartman

CF-75-14

1 February 1976

Float Installation - Water Bombing Operation

CF-77-08

30 September 1977

Reverse Current Relays

CF-79-02

15 February 1979

Torque Tube Attachment Bolts

CF-80-01

1 February 1980

Float Installation - Front Spreader Bar and Struts

CF-81-05

27 February 1981

Electrical Fire Prevention

Compliance:

For Requirements 1 and 2 - Within 12 Months after the effective date of this Directive.

This Airworthiness Directive becomes effective on 31 August 2006.

\n```\n\n| Background: | Recently, a National Airworthiness Authority of a foreign country, to which an ex-Australian registered DHC-6 had been exported, advised CASA that some Transport Canada ADs appeared not to have been complied with. An audit of Australian DHC-6 ADs confirmed that a number of Canadian ADs had not been received during the 1970s and 1980s and that corresponding Australian ADs had not been issued. |\n| ----------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| | The Transport Canada ADs listed in Table 1 of this Directive require one time actions for which the compliance date and/or period has passed. CASA has determined that these ADs may be applicable to Australian registered aircraft. This Directive is issued to ensure all State of Design ADs are complied with. |\n| | CASA appreciates that due to modifications not all the ADs listed in Table 1 will be applicable to all DHC-6 aeroplanes. Transport Canada ADs may accessed via the internet at the following URL:http://www.tc.gc.ca/aviation/applications/cawis-swimn/awd-lv-cs1401.asp?lang=E&rand= |\n\n![](image.001.png) \nJames Coyne \nDelegate of the Civil Aviation Safety Authority\n\n21 July 2006","sortOrder":0},{"sectionNumber":"AD/DHC-6/74","sectionType":"part","heading":"AD/DHC-6/74","content":"## AD/DHC-6/74","sortOrder":1},{"sectionNumber":"State of Design Airworthiness Directives","sectionType":"part","heading":"State of Design Airworthiness Directives","content":"## State of Design Airworthiness Directives","sortOrder":2},{"sectionNumber":"9/2006","sectionType":"part","heading":"9/2006","content":"## 9/2006","sortOrder":3}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":true,"description":"This Directive expands CASA's applied AD scope for Australian‑registered DHC‑6 aircraft by incorporating a set of historic Transport Canada ADs that had not previously been issued in Australia (Background; Table 1). Mechanically, it makes operators responsible for determining applicability and completing any outstanding one‑time actions within 12 months of this Directive (Requirements 1–2; Compliance). The change effectively retroactively imposes compliance obligations for ADs whose original compliance dates had already passed and may affect aircraft differently depending on modifications."},"complexity_factors":["Cross‑jurisdictional reliance on Transport Canada ADs listed in Table 1 rather than full text in the Directive (operators must obtain TC ADs externally).","Vintage and one‑time ADs (effective dates from 1971–1981) with original compliance windows already passed, requiring retroactive assessment and actions.","Applicability uncertainty due to post‑production modifications to individual aircraft — each operator must determine applicability (Requirement 1).","Compliance obligation to perform required AD actions if applicable and not previously done (Requirement 2) within a new 12‑month period from this Directive (Compliance).","Administrative burden to access, interpret and implement foreign ADs and to document compliance; potential material/maintenance work depending on each AD's content.","Limited detail in the Directive about specific corrective measures — substantive actions are defined in the referenced Transport Canada ADs, increasing coordination and information‑gathering needs."],"plain_english_summary":"This Directive requires owners/operators of DHC‑6 (Twin Otter) aeroplanes to check whether the Transport Canada Airworthiness Directives listed in Table 1 apply to their aircraft and, if so and not already done, to carry out the specified actions within 12 months of this Directive (effective 31 August 2006). CASA issued it after an audit found some Canadian ADs had not been received and corresponding Australian ADs were not issued; the owner/operator bears assessment and compliance costs."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This AD serves its original purpose: ensuring Australian-registered aircraft comply with safety directives from the State of Design (Canada). The scope remains tightly focused on addressing a specific historical gap in AD coverage for the DHC-6 fleet."},"complexity_factors":["Single, clearly defined applicability (DHC-6 series aircraft only)","Straightforward two-step compliance requirement: (1) determine applicability, (2) perform actions if applicable","No defined terms section — uses plain technical language","Simple tabular reference to external documents (10 Transport Canada ADs) rather than reproducing complex technical procedures","Single compliance deadline (12 months from effective date)","No nested exceptions, conditional logic, or cross-references to other legislation","Background section provides clear rationale without adding legal complexity"],"plain_english_summary":"This CASA Airworthiness Directive requires Australian owners and operators of DHC‑6 Twin Otter aircraft to review whether 10 Transport Canada airworthiness directives apply to their aircraft and, if so, complete any outstanding mandated work. It closes a safety gap after some Canadian safety notices from the 1970s–80s were not actioned when aircraft were later registered overseas. Affected operators must comply within 12 months of 31 August 2006."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-6-74-state-of-design-airworthiness-directives","history":"/api/acts/ad-dhc-6-74-state-of-design-airworthiness-directives/history","analysis":"/api/acts/ad-dhc-6-74-state-of-design-airworthiness-directives/analysis","conflicts":"/api/acts/ad-dhc-6-74-state-of-design-airworthiness-directives/conflicts","importantCases":"/api/acts/ad-dhc-6-74-state-of-design-airworthiness-directives/important-cases","documents":"/api/acts/ad-dhc-6-74-state-of-design-airworthiness-directives/documents"}}