Definition
A control system in which a small input signal commands a much larger output, with continuous feedback comparing the actual result to the commanded result and automatically correcting any difference. Servo systems are used in aircraft to position flight controls, trim surfaces, autopilot actuators, fuel control units, and other components that require precise, powered movement.
Plain English
A system where a small command tells a powerful device to move something, and the system constantly checks whether the movement matches the command, adjusting itself until it does.
Context Anchor
Seen in powerplant systems where fuel flow, propeller control, or other engine-related parts must respond smoothly and accurately to a control command.
Derivation
From the Latin servus, meaning 'slave' or 'servant.' The idea is that the powerful output device 'serves' the small input signal — doing the heavy lifting on command. This helps explain why a tiny electrical or mechanical input can reliably drive a large physical movement.
Why Pilots Care
Servo systems are how modern aircraft translate small pilot or autopilot inputs into large, precise control movements. Understanding that a servo continuously self-corrects helps explain why autopilot disconnects, runaway trim, or servo failures are treated seriously — the feedback loop is what keeps the output accurate.
Analogy
Power steering is a familiar kind of servo idea: the driver applies a small force at the wheel, and the system uses extra power to move the steering parts. A servo system in an aircraft uses the same basic idea, but for an aircraft component.
Intuition Check
Do not think of a servo system as just any powered system. A servo system uses a command and a check of the actual result to control movement or adjustment accurately.
Example Sentence 1
When the autopilot is engaged, servo systems move the control surfaces to hold the selected heading and altitude.
Example Sentence 2
A faulty servo system in the propeller governor caused the RPM to hunt during cruise.