Safety Publications/Articles

Safety Alert Wake Turbulence

Wake turbulence is common to every aircraft and helicopter. It results from the pressure differential that causes lift. Specifically, as a wing produces lift, an area of high-pressure exists on the bottom of the wing, while a low-pressure area exists on the top of the wing. This pressure differential causes the airflow to roll behind the wing. This vortex, or rolling airmass, is wake turbulence. Its severity depends on the weight, speed, and shape of the wing. It is most pronounced when the aircraft is heavy, slow, and clean.

Since wake turbulence is a by-product of lift, it is present from the time of rotation until the nose wheel touches down on landing. Vortexes tend to sink below and behind the aircraft, so pilots are urged to use caution if operating at a lower altitude than a heavy aircraft. Vortexes can also drift along the ground. This is especially dangerous if there is a crosswind, which can push the vortex and keep it stagnant over the runway. This is most prevalent with a 1- to 5-knot crosswind component.

While air traffic control will try to accommodate a request for wake turbulence avoidance, you should be aware of a few things. For example, once a controller says "Caution - Wake Turbulence," controllers will generally provide no additional guidance. Additionally, if a pilot agrees to visually follow a preceding aircraft, the pilot is responsible for wake turbulence avoidance. When any doubt exists about maintaining safe separation distances between aircraft during approach, ask for updates on separation distance and aircraft groundspeed.

Some Wake Turbulence Avoidance Strategies

• Land beyond the touchdown point of a larger aircraft.
• Land before the rotation point of a larger aircraft.
• Liftoff before the location where a large aircraft rotated. Make an early turnout if necessary.
• Liftoff beyond where a larger aircraft landed.
• If parallel runways are closer than 2,500 feet, be alert for possible wake turbulence drift.
• If intersecting runways are present, note larger aircraft's takeoff or landing point. If larger aircraft is airborne at intersection, avoid flight below its flight path.
• If a larger aircraft makes a go-around, delay takeoff or landing at least two minutes.
• Avoid flight below and behind a larger aircraft by at least 1,000 feet.

Minimum Separation for Small Aircraft

* Assumes takeoff from the same departure threshold.

For more information on wake turbulence, see the Aeronautical Information Manual Chapter 7, Section 3.

View Bruce Landsberg's Safety Pilot articles regarding wake turbulence.