AIRWORTHINESS DIRECTIVE On the commencement date specified below, and for the reasons set out in the background section, the CASA delegate whose signature appears below repeals Airworthiness Directive (AD) AD/DHC-8/48 Amdt 2 and issues the following AD under subregulation 39.001 (1) of CASR 1998 and subsection 33 (3) of the Acts Interpretation Act 1901. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct an 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 DHC-8 Series Aeroplanes AD/DHC-8/48 Amdt 3 Provision of Separate Instrument Grounds 23/2017 Applicability: Bombardier DHC-8 aircraft, Models 102, 103, 106, 201, 202, 301, 311, 314 and 315, serial numbers 3 to 472. Requirement: Carry out de Havilland modification 8/2710 in accordance with de Havilland Alert Service Bulletin A8-34-117, as in force from time to time. Note 1: Transport Canada AD CF-97-01R2 refers. Note 2: The words "as in force from time to time" require compliance with the most recent version of the SB. Compliance: Within 30 days after the commencement date of this AD, unless previously accomplished. Note 3: Previous compliance with the requirement in AD/DHC-8/48 Amdt 2 constitutes compliance with the requirement in this AD. This AD commences on 10 November 2017. Background: Transport Canada advised that simultaneous failures of both the pilot's and co-pilot's Attitude and Heading Reference System have occurred due to a faulty terminal block which provides a common ground connection. The modification details the provision of separate grounds for each instrument. Amendment 3 of this AD is issued to reduce the serial number range in the applicability in accordance with the latest revision of the Canadian AD and also to reference the latest revision of the Canadian AD in Note 1. Ben Wilson Delegate of the Civil Aviation Safety Authority 2 November 2017