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-6/23 Inverter Fuses - Replacement 11/70 Applicability: All models S/Nos. 6 - 427 except S/N 426 & fitted with PC15 & PC15A inverters. Document: De Havilland of Canada SB No. 6/263. Compliance: Before 30 January 1976.