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## Vortex Strength Terminal Area 

Wake turbulence has historically been thought of as only a function of aircraft weight, but recent research considers additional parameters, such as speed, aspects of the wing, wake decay rates, and aircraft resistance to wake, just to name a few. The vortex characteristics of any aircraft will be changed with the extension of flaps or other wing configuration devices, as well as changing speed. However, as the basic factors are weight and speed, the vortex strength increases proportionately with an increase in aircraft operating weight or decrease in aircraft speed. The greatest vortex strength occurs when the generating aircraft is heavy, slow, and clean, since the turbulence from a “dirty” aircraft configuration hastens wake decay. 

## En Route 

En route wake turbulence events have been influenced by changes to the aircraft fleet mix that have more “Super” (A380) and “Heavy” (B-747, B-777, A340, etc.) aircraft 

operating in the NAS. There have been wake turbulence events in excess of 30NM and 2000 feet lower than the wake generating aircraft. Air density is also a factor in wake strength. Even though the speeds are higher in cruise at high altitude, the reduced air density may result in wake strength comparable to that in the terminal area. In addition, for a given separation distance, the higher speeds in cruise result in less time for the wake to decay before being encountered by a trailing aircraft. 

## Vortex Behavior 

Trailing vortices have certain behavioral characteristics that can help a pilot visualize the wake location and take avoidance precautions. 

Vortices are generated from the moment an aircraft leaves the ground (until it touches down), since trailing vortices are the byproduct of wing lift. [Figure 14-46] The vortex circulation is outward, upward, and around the wingtips when viewed from either ahead or behind the aircraft. Tests with large 

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