AIRWORTHINESS DIRECTIVE For the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.001(1) of CASR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section. DHC-6 (Twin Otter) Series Aeroplanes AD/DHC-6/74 State of Design Airworthiness Directives 9/2006 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. 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. 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. 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= James Coyne Delegate of the Civil Aviation Safety Authority 21 July 2006