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 7-3-6.) 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 7-3-7.)

FIG 7-3-7

Vortex Movement in Ground Effect - Tailwind

Tail Wind

Light Quartering
Tailwind

Touchdown Point

7-3-5. Operations Problem Areas
a. A wake turbulence encounter can range from
negligible to catastrophic. The impact of the
encounter depends on the weight, wingspan, size of
the generating aircraft, distance from the generating
aircraft, and point of vortex encounter. The
probability of induced roll increases when the
encountering aircraft"s heading is generally aligned
with the flight path of the generating aircraft.

7-3-4

b. AVOID THE AREA BELOW AND BEHIND
THE WAKE GENERATING AIRCRAFT, ESPECIALLY AT LOW ALTITUDE WHERE EVEN A
MOMENTARY WAKE ENCOUNTER COULD BE
CATASTROPHIC.
NOTE-
A common scenario for a wake encounter is in terminal
airspace after accepting clearance for a visual approach
behind landing traffic. Pilots must be cognizant of their
position relative to the traffic and use all means of vertical

Wake Turbulence