Definition
An electromechanical device in an autopilot system that physically moves a flight control surface (such as the ailerons, elevator, or rudder) or trim system in response to commands from the autopilot computer. Each servo is connected to a specific control axis and applies the force needed to hold or change the aircraft's attitude or heading.
Plain English
The small motor inside the airplane that the autopilot uses to actually move the controls. The autopilot decides what to do; the servo is what does it.
Context Anchor
Seen in autopilot operation and servo failure discussions, especially when the aircraft does not follow autopilot commands correctly or a control feels as if the autopilot is pushing it.
Derivation
From the Latin servus, meaning servant. A servo is literally a 'servant' device — it carries out the orders of the controlling system. Knowing this helps: the servo doesn't think or decide, it just does what the autopilot tells it to do.
Why Pilots Care
A failed servo can cause the autopilot to disengage unexpectedly or apply incorrect control inputs, requiring the pilot to take over manually to maintain safe flight.
Analogy
Think of the autopilot computer as giving the instruction and the servo as the small motor that does the physical pushing or pulling.
Intuition Check
Do not think of the autopilot servo as the whole autopilot. It is the part that turns the autopilot’s commands into actual control movement.
Example Sentence 1
When the autopilot was engaged in heading mode, the aileron servo turned the yoke to bank the aircraft onto the new heading.
Example Sentence 2
The preflight check revealed a faulty autopilot servo, so the pilot disabled the autopilot system for the flight.