COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Bell Helicopter Textron 412 Series Helicopters AD/BELL 412/29 Tail Rotor Driveshaft Hangar Bearings 1/92 DM Applicability: All models fitted with tail rotor driveshaft bearings P/N 204-040-623-003 with S/N prefixed with either "T" or "N" prior to N4000. Requirement: Action in accordance with Bell Alert Service Bulletin 412-91-54 Revision A. Note: FAA Priority Letter AD 91-24-16 refers. Compliance: Daily before first flight of the day after 27 November 1991. Background: A daily inspection of the tailrotor driveshaft bearings has been found necessary following a fatal accident which revealed the possibility of a production batch problem with these bearings.