COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Schweizer (Hughes) 269 Series Helicopters AD/HU 269/106 Main Transmission Pinion Assembly and Ring Gear 2/98 Applicability: All model 269A, 269A-1, 269B, 269C and TH-55A helicopters incorporating main rotor transmissions containing the following pinion assemblies and ring gears, which are installed individually or as a set. P/N 269A5103-31 or -41 pinion assembly identified by the letters EGR, ACR or the manufacturer code number 23751 (EGR) or 57152 (ACR). P/N 269A5104-5 ring gear identified by the letters EGR, ACR or the manufacturer code number 23751 (EGR) or 57152 (ACR). Requirement: Unless previously carried out, inspect the pinion and ring gear teeth in accordance with Schweizer Service Bulletin B-244.2 dated 19 February 1996. Pinion assemblies and ring gears removed from service as a result of this directive shall be permanently retired from service. Note: FAA AD 97-23-06 Amdt 39-10194 refers. Compliance: Before further flight from the effective date should a clicking or tapping sound or other unusual noise or vibration be noted while operating the helicopter or, if a metal particle is found on the magnetic drain plug during routine maintenance. Within the next 50 hours time in service from the effective date. Thereafter, re inspect at intervals not exceeding 50 hours time in service until ring gear P/N 269A5104-5 has been replaced with ring gear P/N 269A5104-7, S/N S2100 or higher. Note Installation of the P/N 269A5104-7 ring gear with S/N S2100 or higher provides terminating action for this directive. This airworthiness directive becomes effective on 29 January 1998. Background: Failure of a gear tooth from the main rotor transmission ring gear have been reported.