oicur12.............
From ICAO 1987 Windshear publication (ICAO Circular 186-AN/122):
Windshear, being the change of wind vector from one point in space to another, is given by the vector difference between the winds at the two points, which itself is a vector(having both speed and direction). The intensity of the shear is calculated by dividing the magnitude of the vector difference between the two points by the distance between them, using consistent units.The calculation of the shear may be done graphically using the triangle of velocities or by subtraction of the components of the two wind vectors either manually or by computer or by trigonometry.
The ICAO guidelines for
unacceptable flight path degradations in windshear are:
Takeoff and approach:
- + or - 15kts IAS
- + or - 500 FPM V/S
- + or - 5 degrees pitch attitude
and:
Approach:
- + or - 1 dot glideslope displacement
- unusual thrust lever position for a significant period of time
Hope this helps.