COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Gulfstream (Grumman American) GA-7 Series Aeroplanes AD/GA-7/9 Rudder Torque Tube Corrosion and Cracking 1/86 T Applicability: All models. Requirement: Action in accordance with Gulfstream Aerospace Corp, SB No ME-21. Compliance: Within 10 hours time in service after 04 December 1985 and thereafter at intervals not exceeding 100 hours time in service or at each issue of a new Maintenance Release. Background: The manufacturer reports instances of corrosion and cracking in the rudder torque tube at the bellcrank area. In two aircraft the torque tube had cracked around the entire circumference of the tube.