COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES DHC-3 (Otter) Series Aeroplanes AD/DHC-3/18 Wing Strut Spar NK Applicability: All models prior to S/No 356. Requirement: Action in accordance with De H Canada EB "O" No 66. Compliance: At intervals not exceeding 250 hours time in service.