COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Eurocopter BK 117 Series Helicopters AD/GBK 117/10 Introduction of a Life Limit on Tail Rotor Drive Bevel Gear 3/98 Applicability: Eurocopter MBB-BK 117 helicopters Serial Number (S/N) 7001 - 7250 (incl) and 7500 - 7509 (incl). Requirement: Enter a life limitation of 18,500 hours against Bevel Gear 117-12215-01(tail rotor (output) drive unit of the main transmission) in the Accessory Replacement Record and Historical Record "Main Transmission". To calculate the replacement time for the installed bevel gear, the total operating time for the component needs to be known. If this is not known, the total operating time for the component shall be considered to be the operating time of the main transmission. Note: LBA AD 97-350 dated 18 December 1997 refers. Compliance: Action must be performed by 31 March 1998. This airworthiness directive becomes effective on 26 February 1998. Background: The working life of the tail rotor (output) drive unit of the main transmission has been recalculated by the manufacturer. This has resulted in the introduction of a life limit on bevel gear part number 117-12215-01 of 18,500 hours.