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. Bombardier (Boeing Canada/De Havilland) DHC-8 Series Aeroplanes AD/DHC-8/117 Rudder Trim Switch Wiring 4/2006 Applicability: DHC-8 Models 401 and 402, serial numbers 4005, 4006, 4008 through 4016 and 4018 through 4058. Requirement: 1. If not previously accomplished, carry out the following in accordance with the Accomplishment Instructions of Bombardier Alert Service Bulletin (ASB) A84-27-13 Revision B, dated 12 January 2002, or later revisions, approved by the Chief, Continuing Airworthiness, Transport Canada: a. Modify the wiring for the rudder trim switch (2722-S2) by incorporating Modsum 4-126256; and b. Visually inspect all wiring on the back of the aileron/rudder trim control panel (P/N 82410608-001, -003 or -005) for chafing. Note 1: Aircraft modified and inspected in accordance with the Accomplishment Instructions of ASB A84-27-13 Revision A, dated 9 January 2002, also satisfy the requirements of this Directive. 2. Replace any chafed wiring found during the Requirement 1.b. inspection. Note 2: Transport Canada AD CF-2002-15 refers. Compliance: For Requirement 1 - Within 30 days after the effective date of this Directive. For Requirement 2 - Before further flight after the Requirement 1.b. inspection. This Airworthiness Directive becomes effective on 13 April 2006. Background: Transport Canada has advised that an investigation of an incident involving rudder trim runaway has revealed a discrepancy in the wiring of the rudder trim control switch on the aileron/rudder trim control panel. The wiring discrepancy in the rudder trim switch could potentially enable a single short circuit on the aileron/rudder trim control panel to cause a runaway condition of the rudder trim actuator James Coyne Delegate of the Civil Aviation Safety Authority 2 March 2006