On the Bombardier Learjet* 20 Series, Learjet 30 Series, Learjet 55, and Learjet 60 aircraft, the horizontal stabilizer actuator is required to be overhauled every 600 hours of operation. These actuators are adjusted and set to very tight tolerances during the overhaul process. These tolerances allow the actuator to operate between a set of electrical stops, which disengage the drive motors. The tolerance from the electrical stop and mechanical abutment is a mere 0.030” to 0.040”.
During installation in the aircraft, the rigging procedure in the AMM (Aircraft Maintenance Manual) should be strictly adhered to. That procedure only allows for adjustment of the main actuator rod end to obtain the correct travel.
During the testing of the installation, if the TO (Take Off) trim indications do not correspond to AMM requirements; the actuator should be returned so the TO trim switches can be correctly adjusted. If the trim indications do not fall within parameters, the potentiometers on the Trim Switch Panel should be adjusted.
There should never be a time during installation, testing, or adjustment when the potentiometer rods on the actuator are adjusted.
Making any changes to these potentiometers runs the risk of the actuator contacting the internal mechanical stops and becoming bound in that position.
A bound actuator will lead to an inoperative trim system and potential safety of flight condition. This will also require costly replacement of the actuator nut and screw assembly.
If you have any questions, please contact me at any time.
* Trademarks of Bombardier Inc. or its subsidiaries.
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