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-6/27 Fuel Cell Sump Plate Flapper Valve Seals - Modification Applicability: All models with S/Nos. 1 to 299 not incorporating Mod. 6/1406. Document: De Havilland of Canada SB No. 6/269. Compliance: Within 100 hours time in service after 30 June 1971. 5/71