Page 594 - PPL-engelsk 2025

Operational procedures

6.9.2 Wake turbulence

All aircrafts create wake vortices when the wings produce lift. Lift is present

when the pressure on the upper side of the wing is less than the pressure on

the underside of the wing.

This pressure difference will try to equalize itself by the air flowing sideways

towards the tip under the wing to equalize with the negative pressure above

the wing.

This results in the formation of a wake. Vortex formation is greatest at low

speed in a pure configuration (without flaps out and with the wheels up).

6.9.2.1 Propagation of edge vortices

So, when an aircraft in the HEAVY category flies below FL 100 and must stay

below 250 Kt, large edge vortices are produced.

As can be seen in the figures here, the

edge vortices spread out to the side and

downwards.

As shown, they exist up to 8 km behind

the aircraft and fall 500 - 900 feet below

the height of the large aircraft.

The risk of and from flying into edge vortices during a flight is normally not very

great.

You can fly for many years without encountering edge vortices. This means that

you don't really think that it is something to fear.

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 594