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/12 Horizontal Stabiliser - Modification NK Applicability: Model 500: S/Nos. 618 to 724 except 700 and 718. Document: 1. Aero Commander SB No. 57; or 2. FAA AD 59-6-1. Compliance: Forthwith.