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AIM

10/12/17

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