COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES DHC-2 (Beaver) Series Aeroplanes AD/DHC-2/20 Control Column Torque Tubes - Inspection 9/80 Applicability: All models DHC-2 and DHC-2 Mk. III. Document: De Havilland Aircraft of Canada SB No. 2/28. Compliance: Initially inspect within 25 hours time in service after 18 September 1980 and thereafter as noted in De Havilland Aircraft of Canada SB No. 2/28. Background: Three overseas operators have reported cracks in the horizontal torque tube at the base of the control column.