Definition
A rapid, repeated variation in the brightness of a light source, caused by quick fluctuations in the current driving it or by mechanical interruption of the light beam. In aviation electrical systems, flicker usually indicates an unstable voltage, a failing component, or a loose connection.
Plain English
A light that quickly blinks or wavers in brightness instead of staying steady.
Context Anchor
Seen during preflight, night flying, cockpit lighting checks, exterior light checks, and when monitoring warning or indicator lights.
Derivation
From Old English 'flicorian,' meaning to flutter or move lightly and quickly. The aviation use keeps the same sense — a light that flutters in brightness rather than holding steady.
Why Pilots Care
Can trigger flicker vertigo, leading to disorientation, nausea, or momentary loss of control if the flash rate falls in the 4–20 Hz range.
Intuition Check
Do not assume a flicker is always an intentional flash. A flicker is usually irregular or unwanted; a normal flashing light is designed to flash that way.
Example Sentence 1
The pilot noticed the panel lights begin to flicker shortly after takeoff and suspected an alternator problem.
Example Sentence 2
At certain propeller RPMs the sun produced a noticeable flicker through the spinning blades.