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-2/29 Elevator Mass Balance Weight 9/97 Applicability: All de Havilland DHC-2 MK I and MK II Beaver aircraft, and all DHC-2 MK III Turbo Beaver aircraft. Requirement: a. For all MK I and MK II Beaver aircraft: Inspect the elevator tip rib for corrosion and install Modification 2/1540 in accordance with instructions contained in de Havilland Service Bulletin 2/50 (Installation of Access Cover and Special Inspection of the Elevator Mass Balance Weight for Separation). b. For all MK III Turbo Beaver aircraft: Inspect the elevator tip rib for corrosion and install Modification T2/2079 in accordance with instructions contained in de Havilland Service Bulletin TB/58 (Installation of Access Cover and Special Inspection of the Elevator Mass Balance Weight for Separation). Note: Transport Canada AD CF-97-06 refers. Compliance: Before 31 January 1998; thereafter at intervals not to exceed 5 years. This airworthiness directive becomes effective on 14 August 1997. Background: Field reports were received of the elevator tip rib corroding underneath the mass balance weights. This corrosion could lead to a loss of the balance weight in flight, and possible flight control difficulties.