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AIM 

6/17/21 

FIG 7

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Wake Encounter Counter Control 

COUNTER 
CONTROL 

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4.  Vortex Behavior 

a. 

Trailing vortices have certain behavioral 

characteristics which can help a pilot visualize the 
wake location and thereby take avoidance precau-
tions. 

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

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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

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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

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5) 

FIG 7

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Wake Ends/Wake Begins 

Touchdown 

Rotation 

Wake Ends 

Wake Begins 

Wake Turbulence 

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