faraim.org

Aeronautical Information Manual (AIM), page 523

Index   522 -- Page 523 -- 524



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

Wake Turbulence 7-3-5

Page 523 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   522 -- Page 523 -- 524