Definition
A closed-loop control system in which a controlling device commands an output, measures the actual result, compares it to the commanded value, and continuously adjusts the output to eliminate any difference between the two. The feedback signal is what makes it a loop rather than a one-way command.
Plain English
A control system that keeps checking its own work. It tells something to move, watches what actually happened, and corrects itself until the result matches what was asked for.
Context Anchor
Seen in autopilot, flight-control, trim, and instrument systems that use automatic correction to move or hold something in position.
Derivation
Servo comes from the Latin servus, meaning 'slave' or 'servant' — the system obediently follows the command it's given. Loop refers to the circular flow of information: command out, result measured, correction back in.
Why Pilots Care
Allows autopilots and stability systems to hold altitude, heading, or attitude without constant manual corrections.
Analogy
Like setting cruise control in a car. You ask for 65 mph, the car checks the actual speed, and adjusts the throttle up or down until it matches — and keeps adjusting as the road changes.
Intuition Check
Do not read “loop” here as an aerobatic loop or a circular flight path. In servo loop, “loop” means a closed automatic control path that checks its own result and corrects it.
Example Sentence 1
When the autopilot is engaged, the servo loop continuously adjusts the elevator position to hold the selected altitude.
Example Sentence 2
During an ILS approach the pitch servo loop kept the aircraft on the glide slope by making small elevator adjustments.