Definition
A change in wind along the flight path that causes an increase in the headwind component (or a decrease in the tailwind component) over a short distance or time. Because airspeed depends on the aircraft's motion through the air, a sudden increase in headwind temporarily raises indicated airspeed and lift, causing the aircraft to balloon above the intended flight path until it re-stabilizes at the new wind condition.
Plain English
A quick change in the wind that pushes more directly against the nose of the aircraft than it was a moment ago. The aircraft briefly feels faster and tends to rise above its intended path until things settle.
Context Anchor
Encountered in instrument weather flying, especially near thunderstorms, fronts, strong surface winds, or other areas where wind speed or direction changes quickly.
Derivation
"Shear" comes from the Old English sceran, meaning to cut or divide. In meteorology it describes the boundary where one layer of air moves differently from another, as if the wind has been "cut" into separate flows. "Headwind shear" is shear that produces a stronger headwind on one side of that boundary.
Why Pilots Care
The sudden airspeed and lift increase can destabilize an approach, requiring immediate pitch and power corrections to avoid an unstable descent or go-around.
Grounding Statement
Picture the airplane flying into air that is suddenly moving more strongly toward its nose; the wing feels more airflow right away.
Intuition Check
Headwind shear does not mean simply flying with a steady headwind. The important part is the sudden change in headwind, because that change can quickly affect airspeed and aircraft control.
Example Sentence 1
On short final, the crew encountered a headwind shear that briefly pushed them above the glide path before the wind eased and they had to add power to recover.
Example Sentence 2
The approach remained stable after the pilot reduced power to compensate for the headwind shear.