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:
- 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.
Overview
The Civil Aviation Regulations 1998, specifically Part 39 - 105, includes Airworthiness Directives for the Gates Learjet 24 & 25 Series Aeroplanes. This directive was enacted to address safety concerns identified by the Federal Aviation Administration (FAA) in the automatic flight control systems of these aircraft models. The primary policy objective of this directive is to ensure the safe operation of the affected aircraft by requiring specific inspections and modifications to the automatic flight control systems, which include the roll, yaw, and pitch axis capstan slip clutches and the stall warning accelerometer unit. Compliance with these directives is mandatory within 50 hours of the aircraft being in service after 25 August 1980, and any discrepancies found during the inspections must be reported to the local Airworthiness office in the form of a Major Defect Report (MDR). These MDRs are then collated and forwarded to the FAA to aid in the ongoing review of the certification basis of Lear aircraft.
Scope and Application
The Civil Aviation Safety Authority (CASA) has issued Airworthiness Directive AD/LEARJET/24, which applies to specific models of Gates Learjet aeroplanes, including all models 24 with serial numbers 24-218 and subsequent; all models 25 with serial numbers 25-003 to 25-061, 25-067 to 25-201, 25-204 and subsequent; all models 28 with serial number 28-001 and subsequent; and all models 29 with serial number 29-001 and subsequent. The directive mandates a series of inspections and modifications to the automatic flight control systems of these aircraft to ensure the capability of manually overriding these systems. The inspections and modifications are necessary to address safety concerns identified during the review of the certification basis of Lear aircraft by the Federal Aviation Administration (FAA), in conjunction with the Gates Learjet Corporation. Compliance with this directive is required within 50 hours of the aircraft being in service after 25 August 1980. Any major defects discovered during the inspection process must be reported to the local Airworthiness office, which will then forward the reports to the FAA. The directive's scope is thus focused on ensuring the airworthiness of specified Learjet models by mandating specific maintenance and inspection procedures, with the ultimate aim of enhancing flight safety.
Key Provisions
The key provisions of the Civil Aviation Regulations 1998, particularly the Airworthiness Directive (AD) pertaining to Gates Learjet 24 & 25 Series Aeroplanes, are outlined in PART 39 - 105. This directive mandates specific inspections and modifications for certain models of Gates Learjet aeroplanes to ensure the safety of automatic flight control systems. Specifically, Section 8/80 of the AD requires inspections to verify the capability of manually overriding the Automatic Flight Control Systems. This includes detailed inspections of the roll, yaw, and pitch axes to ensure proper operation and adjustments as needed.
The directive imposes several obligations on the parties involved, primarily aircraft owners and operators of the specified Gates Learjet models. They must conduct the required inspections within 50 hours of the aeroplane's time in service following 25 August 1980. For the roll axis, if the aircraft is equipped with an FC-110 autopilot, the electrical power must be removed from the autopilot computer, and a temporary resistor must be installed to verify the roll slip clutch breakaway. The yaw and pitch axes also require specific checks and adjustments according to the Gates Learjet Service Manual. In cases where discrepancies are found during these inspections, a Major Defect Report (MDR) must be submitted to the local Airworthiness office. These reports are essential for ongoing safety assessments by the Civil Aviation Safety Authority.
Failure to comply with the requirements set out in the AD may result in serious safety risks, potentially leading to operational issues or accidents. The AD does not explicitly state specific penalties for non-compliance, but non-compliance with airworthiness directives is generally treated seriously under aviation law. Infractions may lead to enforcement actions by the Civil Aviation Safety Authority, which can include fines, suspension or revocation of airworthiness certificates, and other regulatory sanctions. These actions are intended to ensure that all affected aircraft meet the necessary safety standards to protect public safety in aviation.