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/14 Amdt 1 Upper Cabin Door Locking Mechanism - Inspection And Modification 2/80 Applicability: All models 23, 24 and 25 with S/Nos. 23-003 to 23-099, 24-100 to 24-356 and 25-003 to 25-238, with 36 inch cabin door. Document: Gates Learjet SB 23/24/25-280A. Compliance: Within 100 hours time in service after achieving 3000 hours time in service and thereafter as per requirement document or until Gates Learjet Modification Kit No. AMK 78-2 is fitted. Background: Failure of the door locking mechanism during door closing can result in a hidden door unsafe condition.