Definition
An operation or relationship in which the output changes in direct proportion to the input. Doubling the input doubles the output, and a graph of input against output produces a straight line.
Plain English
Something behaves in a linear way when the result goes up or down by the same amount each time you change what goes in. No surprises, no curves -- just a steady, predictable straight-line response.
Context Anchor
Seen in aircraft electronics, sensors, radios, and control systems when describing whether a component responds smoothly and proportionally.
Derivation
From the Latin linea, meaning 'a line.' A linear operation is one whose behaviour, when plotted, produces a straight line -- so the word literally describes the shape of the response.
Why Pilots Care
Pilots rely on instruments and controls behaving linearly so that a small input gives a small, predictable change and a larger input gives a proportionally larger change. Non-linear behaviour can make an instrument or control feel unpredictable, especially near the edges of its range.
Analogy
Think of a volume knob that gets steadily louder as you turn it. If the sound increases smoothly, that is like linear operation. If it suddenly jumps from quiet to loud, it is not acting linearly.
Intuition Check
Do not read “linear” here as just meaning “in a line” or “straight ahead.” In this context, it means the output changes in a steady, proportional way as the input changes.
Example Sentence 1
The sensor has a linear operation across its working range, so each one-degree change in temperature produces the same change in output voltage.
Example Sentence 2
Technicians verify linear operation of the audio amplifier so radio transmissions remain clear and undistorted.