Definition
A wind shear in which the aircraft transitions from a headwind into a tailwind, or from a lighter tailwind into a stronger one, causing a sudden loss of indicated airspeed and a reduction in lift and performance.
Plain English
A quick change in the wind that leaves the aircraft with wind pushing it from behind, which makes the airspeed drop and the airplane sink or struggle to climb.
Context Anchor
Encountered in instrument weather flying when discussing wind shear near storms, during takeoff, and during approach to landing.
Derivation
From 'tailwind' (wind blowing from behind the aircraft, in the direction of flight) and 'shear' (an abrupt change across a boundary). Together: an abrupt change in wind that produces, or increases, a wind from behind.
Why Pilots Care
It produces an abrupt loss of airspeed and climb capability that can place the aircraft below the required glide path or near stall speed if not corrected immediately.
Grounding Statement
Imagine flying into a 20-knot headwind on final approach. Within seconds, the wind swings around and now blows from behind at 10 knots. Your indicated airspeed drops by 30 knots, the wing loses lift, and the airplane begins to sink.
Intuition Check
Do not read tailwind shear as just a normal tailwind. The key idea is the sudden change into more tailwind, or less headwind, which can quickly reduce airspeed.
Example Sentence 1
On short final, the crew encountered a tailwind shear, and the indicated airspeed dropped sharply as the aircraft began to sink below the glidepath.
Example Sentence 2
The departure briefing included the possibility of tailwind shear if a thunderstorm cell moved across the departure path.