Troubleshooting Classic Learjet Spoileron Systems

September 2025

At Duncan Aviation, we frequently receive inquiries regarding troubleshooting classic Learjet spoileron systems. We utilize a straightforward and effective method for diagnosing issues in this area.

Before You Begin:

• Jack the aircraft.
• Connect and prepare a hydraulic mule.

We follow a specific hierarchy for component verification. Always test the system's operation in the following order, ensuring each step is successfully completed before moving to the next.

STEP ONE: Ground Spoilers

Only a few components are required for proper ground spoiler deployment:

• Spoiler solenoid
• Spoiler actuators
• Switch in the pedestal

With 28 VDC and 1500 PSI of hydraulic pressure, the ground spoilers should deploy.

STEP TWO: Air Spoilers

To the components from Step One, add:

• Servo valves on the spoileron manifold
• Spoiler follow-ups

This mode requires 115 VAC. Importantly, air spoilers use the actual squat switches, not the squat switch relay panel. Therefore, pulling the squat switch circuit breaker will not disable this mode of operation.

STEP THREE: Spoileron Mode

Part One: The 25º Flap switches, which activate spoileron mode, essentially create an external jumper circuit to the spoileron computer. Drop the flaps and check for continuity. If continuity is present, proceed to Part Two.

Part Two: Now, incorporate the aileron follow-ups. Move each aileron independently; the on-side spoiler will move up with its respective aileron. Next, add the 16º switches on each side. If either of these switches opens, the spoilerons will fail, triggering an "Aug Ail" or "Spoiler Mon" annunciator, depending on the Learjet model.

It is important to note that this is a simplified troubleshooting method designed to get you started. Always refer to the applicable aircraft maintenance manual for the actual rigging and complete operational checks.

If you have questions about this or any other Learjet technical issue, please do not hesitate to contact me.