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/24 Automatic Flight Controls Systems - Inspection and Modification Applicability: All models 24 with S/Nos. 24-218 and subsequent; All models 25 with S/Nos. 25-003 to 25-061; 25-067 to 25-201, 25-204 and subsequent; All Models 28 with S/Nos. 28-001 and subsequent; All Models 29 with S/Nos. 29-001 and subsequent. 8/80 Requirement: Conduct the following inspections to assure capability of manually overriding the Automatic Flight Control Systems: 1. Energize the aircraft electrical system by applying 28 VDC electrical power. 2. Roll Axis On aircraft equipped with FC-110 autopilot, remove the electrical power from the FC-110 Autopilot Computer. Open the computer and identify the Roll Calibration Board. On the Roll Calibration Board, temporarily install, in parallel with R18 (82 ohm) resistor, a 39 ohm, one watt resistor. Restore the electrical power and engage the Autopilot with the control wheel centered and veify that the roll slip clutch breakaway occurs by rotating the control wheel briskly (45 degrees per second) in both directions. If slippage is not verified, remove the capstan and adjust to proper torque per the appropriate Gates Learjet Service Manual. Return Autopilot Computer to original configuration and accomplish a functional check of the autopilot. 3. Yaw Axis Effective on all Models; Check and adjust the yaw capstan slip clutch torque (primary and secondary where applicable) in accordance with the appropriate Gates Learjet Service Manual. 4. Pitch Axis (a) Effective on Models 24D, 24D-A, 24E, 24F, 24F-A, 25B, 25C, 25D, 25F, 28 or 29 aircraft and aircraft incorporating Gates Learjet Kits AAK71-12 or AMK80-3 (torquers): With the Autopilot disengaged, turn on both stall warning switches and move the control wheel forward and aft at a rapid rate (one second - stop to stop). Note the drag associated with control movement. Turn off the stall warning switches and repeat the rapid fore and aft movement. Note the decrease in drag, which is an indication that the electric disconnect clutch functions properly by disconnecting the drag of the pitch servo (torquer) from the control system. COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES (b) Effective on Models 23, 24, 24B, 24B-A, 24C, 25 and 25A aircraft except aircraft incorporating Gates Learjet Kits AAK71-12 or AMK80-3: Check and adjust the pitch capstan slip clutch for proper torque in accordance with the appropriate Gates Learjet Service Manual. 5. Submit a major defect report (MDR) to the local Airworthiness office if any out of tolerance of roll, yaw or pitch axis capstan slip torque is evident. 6. To assure proper operation of the Stall Warning Accelerometer Unit, perform an inspection of the Stall Warning Accelerometer in accordance with appropriate Gates Learjet Service Bulletin SB 23, 24, 25-301, SB 28, 29-27-3. 7. Submit a major defect report (MDR) to the local Airworthiness office if any discrepancy is discovered during the paragraph 6 inspection. Compliance: Within 50 hours time in service after 25 August 1980. Background: In conjunction with the Gates Learjet Corporation, the Federal Aviation Administration is currently in the process of a review of the adequancy of the certification basis of Lear aircraft, including the adequacy of the certification rules applicable to these type aircraft. While this review is still in its initial stages, preliminary information developed as a result of joint FAA and Gates Learjet Corporation flight evaluations has evidenced characteristics of these aircraft at the limits of their operating envelope which in combination with presently approved operating procedures could adversely affect safety of flight. In light of the foregoing, immediate adoption and effectiveness of this AD is necessary to assure safe operation of the affected aircraft. This AD has been formulated from the FAA produced directive. The flight manual amendments specified in the FAA Directive have been actioned separately. FAA have requested details of any discrepancies found during the inspections hence the request for MDRs to be submitted. The MDRs will be collated by this Department and forwarded to the FAA.