COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Bell Helicopter Textron Canada (BHTC) 407 Series Helicopters AD/BELL 407/7 Tail Rotor Hanger Bearing Support Inspection 5/99 Applicability: Bell (BHTC) Model 407 helicopters serial numbers 53000, 53002 through 53065, 53067 and 53069 through 53075. Requirement: Perform a shimming procedure on the tail rotor hanger bearing support and the bearing hanger on the tail boom in accordance with the procedures specified in BHTC Alert Service Bulletin (ASB) no. 407-97-7 dated 27 February 1997. Note: Transport Canada Airworthiness Directive CF-97-08, dated 08 July 1997 refers. Compliance: At the next scheduled inspection but no later than 01 August 1999. This Airworthiness Directive becomes effective on 20 May 1999. Background: In service reports have shown that some aircraft have developed a gap between the tail rotor hanger bearing support and the bearing hanger on the tail boom. This situation, if not corrected could lead to serious vibration of the tail rotor drive shaft and, eventually, to total disintegration of the shaft. This Directive introduces a shimming procedure to eliminate the gap and the possibility of damaging vibration of the tail rotor drive shaft.