Wake turbulence refers to the chaotic movements of air that follow an aircraft as it moves through the atmosphere. There are two main elements: wingtip vortices and jetwash. Wake turbulence can be dangerous if another aircraft becomes caught in it.
Wingtip vortices are narrow tubes of turbulence that spiral back from the tips of each wing of a plane as they generate lift. They create drag on the aircraft and are also the most important and dangerous component of wake turbulence. Wingtip vortices can remain in the air for up to three minutes and are much more stable than jetwash. Jetwash is the turbulence that occurs as a result of the gasses expelled from the engine of a jet aircraft as it flies. It is mush more chaotic than wingtip vortices, but also much shorter-lived.
Wake turbulence presents a particular threat during landing and take off. During these portions of a flight, the plane moves relatively slowly and at a high angle of inclination, maximizing the formation of wingtip vortices. Planes are also closest together during take off and landing, increasing the possibility of one becoming caught in another's wake. Finally, planes are close to the ground at this time, making recovery difficult in the chance that a plane is caught in wake turbulence.
The International Civil Aviation Organization (ICAO), a branch of the United Nations that governs international air traffic classes aircraft based on its Maximum Take Off Mass (MTOM) and has developed rules to minimize the chance of danger from wake turbulence. According to the ICAO guidelines, planes must wait a minimum time between take off or landing after another aircraft depending upon the MTOM of each plane. The greatest potential danger from wake turbulence occurs when a light aircraft lands following a heavy aircraft. In addition to keeping the recommended distance, the pilot of the light aircraft must stay in line with or above the heavy aircraft's path.