Wind Prediction to Support Reduced Wake Vortex Separation Standars for Closely Spaced Parallel Runway Departures

Air traffic delays were a major problem in the US prior to September 11, 2001, and are expected climb to record levels in the near future. Wake vortex separation standards are an important contributor to the delay problem. Wake vortices are narrow diameter vortices generated as a function of aircraft lift that trail behind an aircraft generating a potential hazard to following aircraft. In certain circumstances, inter-aircraft spacing is increased to alleviate this hazard. The current aircraft separation standards are formulated to keep aircraft safe in the worst case situation, and do not take into account the fact the vortices may have blown out of the way or may have decayed due to atmospheric turbulence. When wake vortex separations are applied, spacing between aircraft is increased from a minimum of 2.5 nm to 4-6 nm (depending on the weight of the following aircraft). This may decrease the number of operations per hour at busy airports to the point that delays result.

Current wake separation standards for parallel runways spaced less than 2500 ft apart, require that they be treated as a single runway for arrivals in poor visibility conditions, and all the time for departures. However, with a steady crosswind the aircraft arriving to or departing from the upwind runway will not encounter the wake from an aircraft operating on the parallel downwind flight path. Thus, wake vortex separation standards are not needed behind the down wind aircraft.

Algorithms to predict when crosswinds will stay strong enough to ensure that wake vortex separations can safely be removed from behind the downwind aircraft departing from closely spaced parallel runways will be discussed. Ideas on extending the initial work to improve reliability and forecast lead time will also be presented.