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aircraft leave the ground, 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 GEN 3.5-18.)
29.4.1.2 The vortex circulation is outward, upward
and around the wing tips when viewed from either
ahead or behind the aircraft. Tests with large aircraft
have shown that the vortices remain spaced a bit less
than a wing span apart, drifting with the wind, at
altitudes greater than a wing span from the ground. In
view of this, if persistent vortex turbulence is
encountered, a slight change of altitude and lateral
position (preferably upwind) will provide a flight
path clear of the turbulence.
29.4.1.3 Flight tests have shown that the vortices
from larger (transport category) 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. Atmospheric
turbulence hastens breakup. Pilots should fly at or
above the preceding aircraft's flight path, altering
course as necessary to avoid the area behind and
below the generating aircraft. However, vertical
separation of 1,000 feet may be considered safe.
(See FIG GEN 3.5-19.)
FIG GEN 3.5-16
Wake Vortex Generation
FIG GEN 3.5-17
Wake Encounter Counter Control
COUNTER
CONTROL
FIG GEN 3.5-18
Wake Ends/Wake Begins
Touchdown Rotation
Wake Ends Wake Begins
30 AUG 07
AIP
United States of America
GEN 3.5-55
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-19
Vortex Flow Field
AVOID Nominally 500-1000 Ft.
Sink Rate
Several Hundred Ft.,/Min.
FIG GEN 3.5-20
Vortex Movement Near Ground - No Wind
No Wind
3K 3K
29.4.1.4 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
3knots. (See FIG GEN 3.5-20.)
29.4.1.5 There is a small segment of the aviation
community that have become convinced that wake
vortices may “bounce” up to twice their nominal
steady state height. With a 200-foot span aircraft, the
“bounce” height could reach approximately 200 feet
AGL. This conviction is based on a single
unsubstantiated report of an apparent coherent
vortical flow that was seen in the volume scan of a
research sensor. No one can say what conditions
cause vortex bouncing, how high they bounce, at
what angle they bounce, or how many times a vortex
may bounce. On the other hand, no one can say for
certain that vortices never “bounce.” Test data have
shown that vortices can rise with the air mass in which
they are embedded. Wind shear, particularly, can
cause vortex flow field “tilting.” Also, ambient
thermal lifting and orographic effects (rising terrain
or tree lines) can cause a vortex flow field to rise.
Notwithstanding the foregoing, pilots are reminded
that they should be alert at all times for possible wake
vortex encounters when conducting approach and
landing operations. The pilot has the ultimate
responsibility for ensuring appropriate separations
and positioning of the aircraft in the terminal area to
avoid the wake turbulence created by a preceding
aircraft.
30 AUG 07
AIP
United States of America
GEN 3.5-56
15 MAR 07
Nineteenth Edition Federal Aviation Administration
FIG GEN 3.5-21
Vortex Movement Near Ground - with Cross Winds
6K
(3K + 3K)
3K Wind
0 (3K - 3K)
FIG GEN 3.5-22
Vortex Movement in Ground Effect - Tailwind
Light Quartering
Tailwind
x
Tail Wind
Touchdown Point
29.4.2 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 GEN 3.5-21.) 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 larger
aircraft upwind from their approach and takeoff flight
paths. (See FIG GEN 3.5-22.)
30 AUG 07
AIP
United States of America
GEN 3.5-57
15 MAR 07
Federal Aviation Administration Nineteenth Edition
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