Definition
A change in wind speed or wind direction over a short distance in the atmosphere. Wind shear can occur in any direction — horizontally, vertically, or both — and may be encountered at any altitude. It is most hazardous near the ground, where rapid changes in airspeed or lift can occur faster than the pilot can correct for them.
Plain English
Wind shear is when the wind suddenly changes speed or direction over a small distance, so the air your aircraft is flying through behaves very differently from the air it was flying through a moment before.
Context Anchor
Pilots encounter wind shear in weather reports, tower or controller alerts, onboard warnings, and during takeoff or landing when the airplane’s airspeed or flight path changes unexpectedly.
Derivation
‘Shear’ comes from Old English ‘sceran’, meaning to cut or divide. The word is used here in the same sense as in engineering — two adjacent layers sliding past each other in different directions or at different speeds, as if cut along a line.
Why Pilots Care
It poses a serious hazard to aircraft control, especially near the ground where there is little time or altitude to recover.
Analogy
It is like driving from smooth pavement onto a patch of ice without warning. The vehicle is the same, but the condition around it changes suddenly, so it reacts differently.
Grounding Statement
Picture an airplane on final approach that suddenly loses headwind and begins to sink lower than expected even though the pilot did not change the controls.
Intuition Check
Wind shear does not mean ordinary gusty wind by itself. The key idea is a sharp change in wind over a short distance, especially a change the airplane flies into suddenly.
Example Sentence 1
Tower reported wind shear on final, so we briefed a go-around and flew the approach with extra airspeed.
Example Sentence 2
Outflow from a thunderstorm created low-level wind shear that turned a headwind into a tailwind during takeoff.