COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
Gates Learjet 35 and 36 Series Aeroplanes
AD/LEARJET 35/15 Automatic Flight Control Systems - Inspection and Modification
9/80
Applicability: All models 35, 36, 35A, 36A with S/Nos. 35-001 and subsequent and 36-001 and subsequent.
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
(a) 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 verify 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.
(b) On aircraft Models 35, 35A, 36 and 36A, conduct the following inspection of the FC-200 autopilot roll axis to assure capability of manually overriding that axis of Automatic Flight Control Systems:
Check and adjust the roll capstan slip clutch for proper torque in accordance with the appropriate Gates Learjet Service Manual.
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
Effective on Models 35, 35A, 36 and 36A aircraft and aircraft incorporating Gates Learjet Kits AAK 71-12 or AMK 80-3 (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
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 35, 36-27-12.
7. Submit a major defect report (MDR) to the local Airworthiness office if any discrepancy is discovered during the paragraph 6 inspection.
Compliance: Paras. 2a, 3, 4 & 6 - Within 50 hours time in service after 25 August 1980.
Para. 2(b) - Within 100 hours time in service after 25 Aug. 1980.
Background: In conjunction with the Gates Learjet Corporation, the Federal Aviation Administration is currently in the process of a review of the adequacy 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, established by the Commonwealth of Australia's Parliament, is a comprehensive legislative instrument designed to ensure the safety and efficiency of civil aviation. Specifically, Part 39 - 105 of the Regulations includes the Schedule of Airworthiness Directives, which sets forth mandatory safety standards and procedures for aircraft maintenance and operation. The enactment of these regulations addresses the critical need for stringent safety protocols in civil aviation to prevent accidents and ensure the reliability of aircraft systems. The Civil Aviation Safety Authority (CASA) issues these directives to mitigate risks associated with the operation of specific aircraft models, such as the Gates Learjet 35 and 36 series aeroplanes, by mandating detailed inspections and modifications to ensure the safe functionality of automatic flight control systems.
The policy objective behind these regulations is to safeguard the public by enforcing rigorous safety standards on aircraft manufacturers and operators. By specifying precise maintenance and inspection procedures, the regulations aim to preempt potential safety hazards and ensure that aircraft remain airworthy. This proactive approach is evident in Airworthiness Directive AD/LEARJET 35/15, which outlines mandatory inspections and modifications for the automatic flight control systems of Gates Learjet 35 and 36 series aeroplanes. The directive requires inspections of the roll, yaw, and pitch axes to verify the capability of manually overriding automatic flight control systems and mandates the submission of major defect reports to the local Airworthiness office to address any discrepancies found during inspections.
Scope and Application
The Civil Aviation Regulations 1998, Part 39 - 105 Civil Aviation Safety Authority Schedule of Airworthiness Directives specifically applies to Gates Learjet 35 and 36 series aeroplanes with serial numbers 35-001 and subsequent for model 35, 35A and 36-001 and subsequent for model 36, 36A. This legislation mandates detailed inspections and modifications to the automatic flight control systems of these aircraft to ensure the capability of manually overriding the systems, particularly focusing on the roll, yaw, and pitch axes. The inspections involve precise steps such as energising the aircraft electrical system, adjusting the roll calibration board and capstan slip clutches, and verifying the operation of the stall warning accelerometer unit, among others. These directives necessitate compliance within specific timeframes post the directive's issue date of 25 August 1980, with varying intervals for different inspections. The legislation further requires the submission of major defect reports to the local Airworthiness office if any discrepancies are found during the inspections, thus facilitating ongoing safety oversight and data collection by both the Australian and U.S. aviation authorities.
Key Provisions
The Civil Aviation Regulations 1998, under Part 39, section 105, include specific Airworthiness Directives (AD) for Gates Learjet 35 and 36 Series Aeroplanes, particularly AD/LEARJET 35/15 concerning the Automatic Flight Control Systems. The directive mandates inspections and modifications to ensure the capability of manually overriding these systems. For instance, Section 2(a) requires the removal of electrical power from the FC-110 Autopilot Computer, followed by the temporary installation of a 39 ohm resistor in parallel with R18. After restoring power, the autopilot must be engaged and the roll slip clutch breakaway must be verified by rotating the control wheel briskly in both directions. If slippage is not verified, adjustments must be made per the Gates Learjet Service Manual. Section 2(b) mandates similar inspections for the FC-200 autopilot roll axis on specified aircraft models. Section 3 necessitates checking and adjusting the yaw capstan slip clutch torque on all models, while Section 4 requires similar inspections and adjustments for the pitch axis on Models 35, 35A, 36, and 36A aircraft and those incorporating specific kits. Section 5 mandates the submission of a Major Defect Report (MDR) to the local Airworthiness office if any axis capstan slip torque is out of tolerance. Section 6 requires an inspection of the Stall Warning Accelerometer, with Section 7 mandating the submission of an MDR if any discrepancies are found during this inspection.
Operators of Gates Learjet 35 and 36 Series Aeroplanes are required to comply with these inspections and modifications to ensure the safety of the aircraft. Specifically, the inspections and adjustments must be conducted within 50 hours for Sections 2(a), 3, 4, and 6, and within 100 hours for Section 2(b) time in service after 25 August 1980. Furthermore, operators must submit MDRs as per Sections 5 and 7 if any discrepancies or out-of-tolerance conditions are identified during the inspections. This includes providing detailed information to the FAA regarding any issues found, as requested.
The Civil Aviation Regulations 1998 impose significant obligations on the operators of Gates Learjet 35 and 36 Series Aeroplanes, particularly in ensuring the safety of the Automatic Flight Control Systems. Failure to comply with the ADs can result in severe consequences. For instance, if any out-of-tolerance conditions are identified during the inspections, an MDR must be submitted to the local Airworthiness office. Non-compliance with these requirements can potentially lead to aircraft being grounded or further safety investigations being conducted, which may result in additional penalties or corrective actions. Additionally, operators must ensure that all inspections and modifications are carried out in accordance with the specified Gates Learjet Service Manuals and Service Bulletins to avoid any breaches of the ADs.