Wake Turbulence Avoidance 1995 Federal Aviation Administration (FAA) Pilot Training Film

more at http://quickfound.net/

Uses re-enactments and animation to illustrate the hazards and physical dynamics of wake turbulence caused by aircraft.

Originally a public domain film, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.

The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).

https://en.wikipedia.org/wiki/Wake_turbulence

Wikipedia license: http://creativecommons.org/licenses/by-sa/3.0/

Wake turbulence is a disturbance in the atmosphere that forms behind an aircraft as it passes through the air. It includes various components, the most important of which are wingtip vortices and jetwash. Jetwash refers simply to the rapidly moving gases expelled from a jet engine; it is extremely turbulent, but of short duration. Wingtip vortices, on the other hand, are much more stable and can remain in the air for up to three minutes after the passage of an aircraft. It is therefore not true turbulence in the aerodynamic sense, as true turbulence would be chaotic. Instead, it refers to the similarity to atmospheric turbulence as experienced by an aircraft flying through this region of disturbed air.

Wingtip vortices occur when a wing is generating lift. Air from below the wing is drawn around the wingtip into the region above the wing by the lower pressure above the wing, causing a vortex to trail from each wingtip. The strength of wingtip vortices is determined primarily by the weight and airspeed of the aircraft. Wingtip vortices make up the primary and most dangerous component of wake turbulence.

Wake turbulence is especially hazardous in the region behind an aircraft in the takeoff or landing phases of flight. During take-off and landing, aircraft operate at high angle of attack. This flight attitude maximizes the formation of strong vortices. In the vicinity of an airport there can be multiple aircraft, all operating at low speed and low altitude, and this provides extra risk of wake turbulence with reduced height from which to recover from any upset...

There is a number of separation criteria for take-off, landing and en-route phases of flight based upon Wake turbulence categories. Air Traffic Controllers will sequence aircraft making instrument approaches with regard to these minima. Aircraft making a visual approach are advised of the relevant recommended spacing and are expected to maintain their own separation.

Notably, the Boeing 757, which by its MTOW falls into Large category, is considered Heavy for purposes of separation because of a number of incidents where smaller aircraft lost control (with some crashing) while following too closely behind a 757.

Common minima are:

Take-off

An aircraft of a lower wake vortex category must not be allowed to take off less than two minutes behind an aircraft of a higher wake vortex category. If the following aircraft does not start its take off roll from the same point as the preceding aircraft, this is increased to three minutes. To put this more generally, an aircraft is usually safer if it is airborne before the rotation point of the airplane that took off before it. However, care must be taken to stay upwind (or otherwise away) from any vortices that were generated by the previous aircraft...