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-6/40 Wing Struts - Inspection and Modification 4/76 Applicability: All models with S/Nos. 1 to 462, 464, 465, 468, 469, 472, 473, 474, 478 and 481. Document: De Havilland of Canada SB No. 6/342. Compliance: 1. Inspect within 120 hours time in service after 31 May 1976. 2. Modify within 360 hours time in service after 31 May 1976.