Modeling of atmospheric effects on wake vortices

When instrument flight rules (IFR) are required due to poor visibility, aircraft are required to remain a minimum distance behind the preceding aircraft, with the result that airport capacity can be adversely affected. In certain atmospheric conditions (e.g., strong cross winds), this minimum distance is greater than it needs to be for safe operations. If it could reliably be determined when minimum following distances can be reduced, then airport capacity during IFR could be increased.

We have developed an approach to modeling the evolution of aircraft wake vortices which can be used to predict the length of time that wake vortices will remain a hazard to following aircraft. In this approach, atmospheric conditions are represented by vertical profiles of potential temperature, cross wind, and turbulence. Either eddy dissipation rate (EDR) or turbulence kinetic energy (TKE) can be used to characterize the turbulence. The wake vortices are characterized by their initial position, lateral separation, and initial descent speed. The model has been used by the NASA Langley Research Center as the predictor component in a prototype system (called AVOSS for Aircraft VOrtex Spacing System) that could be used by air traffic control to determine when it is acceptable to reduce aircraft spacing.

In this paper, we describe our modeling approach and show examples of how various atmospheric conditions can be expected to affect the evolution of aircraft wake vortices.