AIM
4/3/14
7−3−5
Wake Turbulence
7
−
3
−
5. Operations Problem Areas
a.
A wake encounter can be catastrophic. In 1972
at Fort Worth a DC−9 got too close to a DC−10
(two miles back), rolled, caught a wingtip, and
cartwheeled coming to rest in an inverted position on
the runway. All aboard were killed. Serious and even
fatal GA accidents induced by wake vortices are not
uncommon. However, a wake encounter is not
necessarily hazardous. It can be one or more jolts with
varying severity depending upon the direction of the
encounter, weight of the generating aircraft, size of
the encountering aircraft, distance from the generat-
ing 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.
b.
AVOID THE AREA BELOW AND BEHIND
THE GENERATING AIRCRAFT, ESPECIALLY
AT LOW ALTITUDE WHERE EVEN A
MOMENTARY WAKE ENCOUNTER COULD BE
HAZARDOUS. This is not easy to do. Some
accidents have occurred even though the pilot of the
trailing aircraft had carefully noted that the aircraft in
front was at a considerably lower altitude. Unfortu-
nately, this does not ensure that the flight path of the
lead aircraft will be below that of the trailing aircraft.
c.
Pilots should be particularly alert in calm wind
conditions and situations where the vortices could:
1.
Remain in the touchdown area.
2.
Drift from aircraft operating on a nearby
runway.
3.
Sink into the takeoff or landing path from a
crossing runway.
4.
Sink into the traffic pattern from other airport
operations.
5.
Sink into the flight path of VFR aircraft
operating on the hemispheric altitude 500 feet below.
d.
Pilots of all aircraft should visualize the
location of the vortex trail behind larger aircraft and
use proper vortex avoidance procedures to achieve
safe operation. It is equally important that pilots of
larger aircraft plan or adjust their flight paths to
minimize vortex exposure to other aircraft.
7
−
3
−
6. Vortex Avoidance Procedures
a.
Under certain conditions, airport traffic control-
lers apply procedures for separating IFR aircraft. If a
pilot accepts a clearance to visually follow a
preceding aircraft, the pilot accepts responsibility for
separation and wake turbulence avoidance. The
controllers will also provide to VFR aircraft, with
whom they are in communication and which in the
tower’s opinion may be adversely affected by wake
turbulence from a larger aircraft, the position, altitude
and direction of flight of larger aircraft followed by
the phrase “CAUTION − WAKE TURBULENCE.”
After issuing the caution for wake turbulence, the
airport traffic controllers generally do not provide
additional information to the following aircraft
unless the airport traffic controllers know the
following aircraft is overtaking the preceding
aircraft. WHETHER OR NOT A WARNING OR
INFORMATION HAS BEEN GIVEN, HOWEVER,
THE PILOT IS EXPECTED TO ADJUST AIR-
CRAFT OPERATIONS AND FLIGHT PATH AS
NECESSARY TO PRECLUDE SERIOUS WAKE
ENCOUNTERS. When any doubt exists about
maintaining safe separation distances between
aircraft during approaches, pilots should ask the
control tower for updates on separation distance and
aircraft groundspeed.
b.
The following vortex avoidance procedures are
recommended for the various situations:
1. Landing behind a larger aircraft
− same
runway.
Stay at or above the larger aircraft’s final
approach flight path−note its touchdown point−land
beyond it.
2. Landing behind a larger aircraft
− when
parallel runway is closer than 2,500 feet.
Consider
possible drift to your runway. Stay at or above the
larger aircraft’s final approach flight path− note its
touchdown point.
3. Landing behind a larger aircraft
− crossing
runway.
Cross above the larger aircraft’s flight path.
4. Landing behind a departing larger air-
craft
− same runway. Note the larger aircraft’s
rotation point− land well prior to rotation point.
5. Landing behind a departing larger air-
craft
− crossing runway. Note the larger aircraft’s
rotation point− if past the intersection− continue the
approach− land prior to the intersection. If larger
aircraft rotates prior to the intersection, avoid flight