COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Aerospatiale (Socata) TB20 (Trinidad) Series Aeroplanes AD/TB20/20 Horizontal Stabiliser Balance Weight 4/91 DM Applicability: Model TB20 and TB21 series with serial numbers 1 through 1030. Requirement: Action in accordance with Alert SB 57. Compliance: Within 25 hours time in service after 13 February 1991. Background: This Directive requires an inspection to determine whether both attaching nuts of the horizontal stabilizer balance weight are within the required safety dimension. Detachment of balance weight may lead to a dangerous flutter condition.