COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Twin Commander (Gulfstream/Rockwell/ Aerocommander 500, 600 and 700) Series Aeroplanes AD/AC/9 Vertical and Horizontal Stabiliser - Spar NK Reinforcement Applicability: Models 500, 560, 560A, 560E, 680, 680E, 720: S/Nos. 151 to 710. Document: 1. Aero Commander SB No. 50; or 2. FAA AD 59-4-1. Compliance: Forthwith.