Definition
A control method, commonly called PID, used in automatic flight and engine control systems that calculates corrections based on three combined factors: the size of the current error (proportional), the accumulated error over time (integral), and the rate at which the error is changing (derivative). The system blends these three terms to produce smooth, accurate, and stable corrections to a controlled value such as heading, altitude, or engine speed.
Plain English
A way for an automatic system to fix an error by looking at three things at once: how big the error is right now, how long it has been off, and how fast it is changing. Combining these gives a steady, accurate correction without overshooting or hunting back and forth.
Context Anchor
Seen in discussions of autopilot behavior, automatic flight control, stability systems, and electronic control tuning.
Derivation
The name comes straight from the three mathematical terms it uses. 'Proportional' (from Latin proportio, 'in relation to') means the correction is sized in proportion to the error. 'Integral' (from Latin integralis, 'whole') means it adds up the error over time. 'Derivative' (from Latin derivare, 'to draw off from') refers to the rate of change. Knowing the three names tells you exactly what the controller is paying attention to.
Why Pilots Care
PID logic keeps autopilots stable and precise, preventing constant hunting or drifting that would otherwise require constant manual correction.
Analogy
It is like steering back to the center of a lane: you look at how far off-center you are now, how long you have been drifting, and whether the drift is speeding up or slowing down. A Proportional-Integral-Derivative controller does that kind of correction automatically.
Intuition Check
Do not read this as three separate aircraft parts. In this context, Proportional-Integral-Derivative names one control method made of three ways of deciding a correction.
Example Sentence 1
The autopilot uses a proportional-integral-derivative controller to hold the selected altitude without overshooting or oscillating.
Example Sentence 2
Technicians tuned the proportional-integral-derivative parameters on the fuel control unit to improve throttle response during climb.