Definition
The hinged control surface on the trailing edge of the left wing that moves up or down to change the lift produced by that wing, causing the airplane to roll about its longitudinal axis. The left and right ailerons move in opposite directions: when the left aileron deflects upward, the right aileron deflects downward, and vice versa.
Plain English
A flap on the back edge of the left wing that tilts up or down to roll the airplane left or right. It always works in the opposite direction to the matching flap on the right wing.
Context Anchor
Seen in aircraft control diagrams, preflight control checks, and discussions of roll control.
Derivation
Aileron comes from the French word for 'little wing,' from aile meaning 'wing.' That image fits well: the aileron is a small movable section at the outer trailing edge of the wing that changes how much lift that wing produces.
Why Pilots Care
Deflecting the left aileron is the primary way a pilot initiates and controls roll during turns and attitude changes.
Intuition Check
“Left” means the airplane’s left side as seen from the pilot’s seat facing forward, not the left side of someone standing in front of the airplane looking at it.
Example Sentence 1
When the pilot turned the control wheel to the right, the left aileron deflected downward and the right aileron deflected upward, rolling the airplane into a right bank.
Example Sentence 2
During the preflight inspection the student confirmed the left aileron moved freely in both directions.