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-3/7 Engine Breather Drain Box NK Applicability: All models with S/Nos 1 to 73. Requirement: Action in accordance with De H Canada EB "O" No 5. Note: Canadian AD 55-6 refers. Compliance: Forthwith.