Definition
The tendency of an airplane on the ground to turn into the wind, caused by the wind acting on the larger side surface area behind the main wheels (mainly the vertical fin and rear fuselage), which pivots the nose toward the wind direction.
Plain English
When the wind blows from the side, the airplane on the ground naturally wants to swing its nose around to point into the wind, like a weather vane on a roof.
Context Anchor
Encountered during ground handling, especially crosswind taxiing, takeoffs, and landings.
Derivation
From 'weather vane,' the rooftop arrow that pivots to point into the wind. An airplane sitting on its wheels behaves the same way because there is more surface area behind its pivot point than in front of it, so the wind pushes the tail downwind and swings the nose into the wind.
Why Pilots Care
Uncorrected weathervaning can lead to loss of directional control and ground loops, especially in tailwheel aircraft.
Analogy
Like a weather vane on a barn roof: the wind always pushes the tail around so the arrow points into the wind. An airplane on its wheels does the same thing for the same reason.
Grounding Statement
With wind from the left during a landing roll, the airplane may try to turn left unless the pilot corrects it.
Intuition Check
Weathervaning does not mean the airplane is being blown straight sideways. It means the airplane is trying to turn its nose into the wind.
Example Sentence 1
During taxi in a strong crosswind, the pilot held aileron into the wind and used rudder to counter the airplane's tendency to weathervane.
Example Sentence 2
After touchdown the airplane began weathervaning into the wind, requiring immediate corrective rudder input.