Definition
A control or correction response in which the size of the response is directly related to the size of the error being corrected. The larger the deviation from the desired condition, the larger the corrective action; the smaller the deviation, the smaller the correction. This is the defining characteristic of proportional control in autopilots, flight control augmentation systems, and electronic feedback circuits.
Plain English
The further off you are, the bigger the fix. A small mistake gets a small correction; a big mistake gets a big correction.
Context Anchor
Seen in discussions of automatic control systems, autopilots, flight directors, and aircraft instruments that compare a desired value with an actual value.
Derivation
Proportional comes from the Latin proportio, meaning 'in relation to' or 'in comparison with.' Magnitude comes from the Latin magnitudo, meaning 'size' or 'greatness.' Together the phrase means 'in direct relation to the size of the error.'
Why Pilots Care
Ensures smooth return to desired flight path without over-correction or oscillation.
Analogy
Like steering a car: if you drift slightly out of your lane you nudge the wheel a little, but if you drift a lot you turn it more. The size of your steering input matches the size of the drift.
Grounding Statement
A small altitude difference calls for a small correction; a large altitude difference calls for a larger correction.
Intuition Check
Do not read “error” here as a personal mistake. In this context, error means the measured difference between where the system is and where it is supposed to be. “Magnitude” means the size of that difference, not its direction.
Example Sentence 1
The autopilot's pitch correction is proportional to the magnitude of the error, so a small altitude deviation produces only a slight elevator movement.
Example Sentence 2
Damping in the attitude indicator system is designed proportional to the magnitude of the error to prevent unwanted oscillations.