AIRWORTHINESS DIRECTIVE On the effective date specified below, and for the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/DHC-8/137 and issues the following 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-8/137 Amdt 1 Wing Front Spar to Fuselage Attachment 8/2008 Applicability: DHC-8 aircraft, Models 400, 401, and 402, serial numbers 4001, and 4003 through 4176. Requirement: Action in accordance with the requirements of Transport Canada Emergency AD CF-2008-11R1. Note: Bombardier Inc. Alert Service Bulletins (ASB) A84-57-19 original issue, A84-57-19 Revision A, and A84-57-19 Revision B, or later Transport Canada approved revisions, refer. Compliance: As specified in the Requirement document, with a revised effective date of 31 July 2008. Note: The revised effective date of the original issue of this Directive was 8 February 2008. This Amendment becomes effective on 31 July 2008. Background: During scheduled maintenance, an operator found cracks in the DSC228-16 barrel nut at one of the four primary front spar wing to fuselage attachment joints. The investigation determined that the cracks were due to hydrogen embrittlement and the problem is believed to be restricted to a batch of 166 barrel nuts from one supplier. Further inspection by a different operator revealed that cracked barrel nuts were found at three of the four wing front spar to fuselage joints on the same aircraft. All three barrel nuts were from the suspect batch. Failure of the barrel nuts could compromise the integrity of the wing to fuselage attachments. Amendment 1 is issued in response to a new Transport Canada AD, which mandates the removal of the affected barrel nuts and the application of corrosion inhibiting compound in accordance with ASB A84-57-19 Revision B, dated 6 March 2008. David Villiers Delegate of the Civil Aviation Safety Authority 12 June 2008