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-2/21 Flight Controls, Elevator Root Rib - Inspection 10/80 Applicability: All Model DHC-2 Mk. I, Mk. II and Mk. III. Document: De Havilland Aircraft of Canada SB No. 2/30. Compliance: Within 100 hours time in service after 31 December 1980 and thereafter at intervals not exceeding 400 hours time in service. Background: Cracking of the elevator root rib at the torque tube attachment and cracking of the reinforcing doubler in the same area has been reported to the manufacturer.