COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Robinson R44 Series Helicopters AD/R44/6 Main Rotor Gearbox 12/96 DM Applicability: This Directive is applicable to all R44 helicopters with S/N 0001 through 0232 fitted with main rotor gearbox P/N C006-1 Revision A through P. Helicopters S/N 0019, 0067, 0118, 0135 and 0215 are already in compliance with this Directive. Requirement: Unless previously carried out, action in accordance with Robinson R44 SB No 15 dated 2 August 1996. Report any fretting or loose bolts by MDR action. Note: FAA Priority Letter AD 96-18-22 refers. Compliance: Within 100 hours time in service from 11 September 1996 or prior to 1 October 1996, whichever occurs first. Background: An overseas inflight failure of a main rotor gearbox has been reported. Inspection of the gearbox revealed that the 18 bolts securing the ring gear, P/N C146-3, to the gear carrier, P/N C268-2, had lost clamping torque which then resulted in fretting and failure of the gear carrier.