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 412/27 Tailboom Upper Longeron 12/90 DM Applicability: Model 412 with serial numbers: 33001 through 33211 34001 through 34013 36001 through 36013 Requirement: 1. Action in accordance with Part 1 of Bell Alert Service Bulletin No 412-90-49. 2. Action in accordance with Part II of Bell Alert Service Bulletin No 412-90-49. Compliance: 1. Prior to 30 November 1990. 2. At intervals not exceeding 300 hours time in service after incorporation of Requirement 1. Background: Incidents of cracked longeron splices have created a requirement for additional access to inspect upper longeron splices, and modification action to increase structural integrity.