When do wake vortices begin and end?

7-4-4. Vortex Behavior
a. Trailing vortices have certain behavioral characteristics which can help a pilot visualize the wake location
and thereby take avoidance precautions.
1. An aircraft generates vortices from the moment it rotates on takeoff to touchdown, since trailing vortices
are a by-product of wing lift. Prior to takeoff or touchdown pilots should note the rotation or touchdown point
of the preceding aircraft. (See FIG 7-4-3.)
2. The vortex circulation is outward, upward and around the wing tips when viewed from either ahead or
behind the aircraft. Tests with larger aircraft have shown that the vortices remain spaced a bit less than a wingspan
apart, drifting with the wind, at altitudes greater than a wingspan from the ground. In view of this, if persistent
vortex turbulence is encountered, a slight change of altitude (upward) and lateral position (upwind) should
provide a flight path clear of the turbulence.
3. Flight tests have shown that the vortices from larger aircraft sink at a rate of several hundred feet per
minute, slowing their descent and diminishing in strength with time and distance behind the generating aircraft.
Pilots should fly at or above the preceding aircraft's flight path, altering course as necessary to avoid the area
directly behind and below the generating aircraft. (See FIG 7-4-4.) Pilots, in all phases of flight, must remain
vigilant of possible wake effects created by other aircraft. Studies have shown that atmospheric turbulence
hastens wake breakup, while other atmospheric conditions can transport wake horizontally and vertically.
4. When the vortices of larger aircraft sink close to the ground (within 100 to 200 feet), they tend to move
laterally over the ground at a speed of 2 or 3 knots.  (See .FIG 7-4-5)
Wake Turbulence 7-4-2

2/20/25 AIM
FIG 7-4-3
Wake Ends/Wake Begins
Touchdown Rotation
Wake Ends Wake Begins
FIG 7-4-4
Vortex Flow Field
AVOIDAVOID Nominally 500-1000 Ft.Nominally 500-1000 Ft.
Sink Rate
Several Hundred Ft.,/Min.
Sink Rate
Several Hundred Ft.,/Min.

FIG 7-4-5
Vortex Movement Near Ground - No Wind
No WindNo Wind
3K3K 3K3K
Wake Turbulence 7-4-3

6K
AIM 2/20/25
FIG 7-4-6
Vortex Movement Near Ground - with Cross Winds
3K Wind3K Wind
6K 0 (3K - 3K)0 (3K - 3K)
(3K + 3K)(3K + 3K)
5. Pilots should be alert at all times for possible wake vortex encounters when conducting approach and
landing operations. The pilot is ultimately responsible for maintaining an appropriate interval, and should
consider all available information in positioning the aircraft in the terminal area, to avoid the wake turbulence
created by a preceding aircraft. Test data shows that vortices can rise with the air mass in which they are
embedded. The effects of wind shear can cause vortex flow field "tilting." In addition, ambient thermal lifting
and orographic effects (rising terrain or tree lines) can cause a vortex flow field to rise and possibly bounce.
b. A crosswind will decrease the lateral movement of the upwind vortex and increase the movement of the
downwind vortex. Thus, a light wind with a cross-runway component of 1 to 5 knots could result in the upwind
vortex remaining in the touchdown zone for a period of time and hasten the drift of the downwind vortex toward
another runway. (See FIG 7-4-6.) Similarly, a tailwind condition can move the vortices of the preceding aircraft
forward into the touchdown zone. THE LIGHT  QUARTERING TAILWIND REQUIRES MAXIMUM
CAUTION. Pilots should be alert to large aircraft upwind from their approach and takeoff flight paths. (See
FIG 7-4-7.)
Wake Turbulence7-4-4

2/20/25 AIM
FIG 7-4-7
Vortex Movement in Ground Effect - Tailwind
Light Quartering
Tailwind
Light Quartering
Tailwind
x
Tail WindTail Wind
Touchdown PointTouchdown Point