COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Robinson R22 Series Helicopters AD/R22/13 Tail Rotor Drive Shaft - Replacement 8/82 Applicability: Models R22 with S/Nos. 0002 to 0282. Document: Robinson SB.21. Compliance: Within 100 hours time in service after 30 September 1982. Background: There have been reported cases of tail rotor drive shaft whipping, due to inadvertent rotor overspeed. A higher frequency shaft is introduced to reduce the possibility of drive shaft whip, and subsequent failure.