COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES DHC-6 (Twin Otter) Series Aeroplanes AD/DHC-6/61 Amdt 1 Applicability: All models. Wing Main Spar Lower Cap Angles 7/91 Requirement: Action in accordance with the Technical Requirements of Transport Canada AD CF- 87-02, R1. Note: De Havilland SB 6/492 Revision A refers. Compliance: As specified in the Requirement Document with a revised effective date of 11 July 1991 for Australian registered aircraft. Background: Exfoliation corrosion in the main spar cap lower angles has been reported on older aircraft. Amendment 1 is raised to reflect a revision of the related Country of origin AD which was issued to remove flight hour limitations from the compliance time requirements.