COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Robinson R44 Series Helicopters AD/R44/13 Rotor Drive Yoke 10/99 DM Applicability: All Model R44 helicopters. Requirement: 1. Determine, by inspection, if the yoke assembly, part number (P/N) C908-1C, from Lot No. 36B, 37, or 38 is installed. Note 1: Yoke assemblies, P/N C908-1C, from Lot Nos. 36B, 37, and 38 were installed as original equipment in R44 helicopters, Serial Numbers 0219 and 0535 through 0608 (except numbers 0565, 0582, and 0592). 2. Replace any yoke assembly, P/N C908-1C, from Lot No. 36B, 37, or 38, with a serviceable yoke assembly from a lot other than 36B, 37, or 38 in accordance with the compliance procedure, steps 2 through 12, of Robinson Helicopter Company R44 Service Bulletin SB-35, dated July 26, 1999. Note 2: Priority Letter FAA AD 99-17-17 refers. Compliance: Before further flight after 25 August 1999, unless already accomplished. This Airworthiness Directive becomes effective on 25 August 1999. Background: The FAA received a report of an incident in which, during cruise flight, the pilot heard a loud bang and noticed no tail rotor effectiveness after entering autorotation. An investigation revealed that the yoke assembly P/N C908-1C, which connects the main rotor gearbox pinion shaft to the forward flexplate, had failed at a weld joint due to a crack. The cause of the crack is unknown, but still under investigation. Robinson Helicopter Company has identified the manufacturing lots associated with the failed yoke. Failure of the yoke assembly could result in loss of main and tail rotor drive and subsequent loss of control of the helicopter.