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-6/46 Amdt 4 Flap Operating Rod Assemblies and Control Rods 2/92 Applicability: Model DHC-6 series. Requirement: Action in accordance with the technical requirements of Transport Canada AD CF- 79-22 R1. Note: De Havilland SB 6/388 Revision C and SB 6/502 refers. Compliance: As specified in the Requirement Document with a revised effective date of 3 February 1992 for Australian registered aircraft. The compliance of the previous issue of this Directive was "as per Requirement Document". Background: Instances of stress-corrosion cracking have occurred on original equipment 2024-T3 alloy flap control rods. Amendment 4 introduces SB 6/502 and the appropriate inspection interval for 6061-T6 control rods pursuant to Transport Canada's Aging Aircraft program. The effective date required by Transport Canada is extended by four months.