COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Gulfstream (Grumman) G1159 and G-IV Series Aeroplanes AD/G1159/18 Ground Spoiler System - Deactivation 12/75 Applicability: All models not modified in accordance with Grumman Aircraft Service Change No. 180. Document: FAA AD 74-17-05 Amendment 39-2359. Compliance: Within 10 hours time in service after 18 November 1975.