Windshear is a sustained change in wind velocity along the flight path of an aircraft. It occurs significantly faster than the aircraft can accelerate or decelerate. It is usually present with the following weather phenomena; Thunderstorms, Microbursts, Fronts, Temperature inversions, Terrain or buildings.
It can occur at any level, but usually affects aircraft taking off or landing from the surface to a height of about 1500ft. Windshear can increase or decrease the speed and vertical speed of the aircraft, as well as drift it from side to side.
Windshear should be reported to arriving and departing aircraft until it is included on the ATIS (Some aerodromes require it to be passed even if it is included on the ATIS).
When a pilot reports windshear, they should include:
When informing aircraft of windshear, the following phraseology should be used: "At (time) a departing/arriving (a/c type) reported windshear at (altitude). Airspeed loss/gain (number) knots, strong left/right drift."
Windshear should be reported until there are no further reports of windshear.