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 117/4 Landing Gear Electrical Bonding 12/91 Applicability: All MBB-BK 117 aircraft serial No 7001 through 7261 inclusive. Requirement: Action in accordance with MBB Alert SB 117 -90-104. Compliance: Within 50 hours time in service after 12 December 1991. Background: The existing bonding of the landing gear to the helicopter has been determined by the manufacturer to be inadequate to ensure satisfactory elimination of electrostatic charges.