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/25 Automatic Flight Control System - Deactivation and Modification Applicability: All models 24 with S/Nos. 24-100 and subsequent; All models 25 with S/Nos. 25-003 and subsequent; All models 28 with S/Nos. 28-001 and subsequent; All models 29 with S/Nos. 29-001 and subsequent. 4/81 Requirement: 1. Deactivate the pitch function of the FC-110 Automatic Flight Control System (AFCS) or Automatic Flight Control Stability System (AFC/SS), as indicated below, by pulling the AFCS Pitch DC Circuit Breaker to the off position, banding it to prevent use of this function and checking to assure this function is the only deactivated circuit or control. SERIES SERIAL NUMBERS LOCATION 24 100 thru 139 (except 131, 132 Pilot's Sub Panel & 134) 131, 132 & 134 Pilot's circuit breaker panel 140 thru 229 Autopilot computer rack (under pilot's seat) 230 and up Pilot's circuit breaker panel. 25 003 thru 069 (except 032) Autopilot computer rack (under pilot's seat) 032 Pilot's Sub Panel 070 and up Pilot's circuit breaker panel 28 001 and up Pilot's circuit breaker panel 29 001 and up Pilot's circuit breaker panel COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES 2. Install a locally fabricated placard on or near the autopilot control head in clear view of the crew using letters at least 3/32 inch high, which reads: AUTOPILOT PITCH AXIS INOPERATIVE OBSERVE APPROPRIATE AFM AIRSPEED LIMITATIONS FOR INOPERATIVE AUTOPILOT and operate the airplane in accordance with this placard. 3. Visually inspect the elevator control system to assure that Pitch Axis Servo (DC Torquer), P/N 6600163-( ) is installed. (a) If installed, modify the airplane by incorporating autopilot pitch trim monitor test switch in accordance with Gates Learjet Airplane Modification Kit AMK 80-16B, Change 2. (b) If not installed, modify the airplane by replacing the pitch servo actuator and capstan and incorporating autopilot pitch trim monitor test switch in accordance with Gates Learjet Airplane Modification Kits AMK 80-3, Change 4, and AMK 80-16B, Change 2, respectively. 4. When paragraph 3 of this AD has been accomplished, the requirements of paragraphs 1 and 2 of this AD are no longer applicable. Compliance: For paras. 1 and 2 - Before further flight. For Para. 3 - Before 1 May 1981. Background: This action is necessary to reduce the hazard created by a possible pitch axis malfunction which if not detected, could result in a hazardous flight attitude.