COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Gates Learjet 24 & 25 Series Aeroplanes AD/LEARJET/27 Horizontal Stabiliser Hinge Pin Bushing Installation - Inspection 12/81 Applicability: All Gates Learjet models 24 and 25 with S/Nos. referenced in Gates Learjet Service Bulletin No. 23/24/ 25-311 or with S/Nos. referenced in subsequent issues of that Service Bulletin. Document: Gates Learjet SB 23/24/25-311. Compliance: Within 100 hours time in service after 31 December 1981. Background: The horizontal stabiliser hinge pin bushings may move out of their mating fittings during normal service.