COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Bell Helicopter Textron Canada (BHTC) 206 and Agusta Bell 206 Series Helicopters AD/BELL 206/107 Main Rotor Mast 8/87 DM Applicability: All Model 206A, 206B, 206L, 206L-1 and 206L-3 helicopters fitted with main rotor mast P/N 206-010-332-121 or P/N 206-040-535-105 with serial numbers listed in the Requirement Documents. Requirement: Remove from service those masts listed in the following documents: For models 206A and 206B: Bell Alert Service Bulletin 206-87-37. For models 206L series: Bell Alert Service Bulletin 206L-87-44. Note: FAA Telex AD 87-10-11 refers. Compliance: Within 25 hours time in service after 1 June 1987. Background: A batch of main rotor masts has been manufactured from material lots which may contain metallurgical imperfections. These inclusions may degrade the fatigue properties of the masts and could lead to catastrophic failure in flight.