Definition
The aileron on the wing facing into the wind, deflected upward by the pilot during taxi in a crosswind to keep that wing from being lifted by the wind. The control wheel or stick is held toward the wind, which raises the upwind aileron and lowers the downwind aileron.
Plain English
The aileron on the side the wind is coming from. While taxiing in a crosswind, the pilot turns the control wheel into the wind so this aileron points up, helping hold the wing down so the wind cannot lift it.
Context Anchor
Seen in taxi instructions for holding the flight controls correctly when wind is blowing across or partly across the airplane.
Derivation
Upwind means 'toward the side the wind is coming from.' Aileron comes from French for 'little wing.' Together: the little wing-control surface on the side facing the wind.
Why Pilots Care
Prevents the upwind wing from being lifted by crosswind, reducing the risk of loss of directional control or tipping during ground operations.
Grounding Statement
Picture wind hitting the airplane from the left: the left wing is the upwind wing, so the left aileron is the upwind aileron.
Intuition Check
Upwind does not mean the direction the airplane is moving. It means the side the wind is coming from.
Example Sentence 1
Taxiing toward the run-up area in a left crosswind, the pilot held the control wheel to the left to keep the upwind aileron deflected up.
Example Sentence 2
The checklist reminded the pilot to apply full upwind aileron deflection before entering the taxiway in gusty conditions.