Statistical Separation Standards for the Aircraft-Approach Process

Demand for air transportation has been increasing. A response to this is enhancing the runway utilization and throughput before investing on new runways or instruments. Runway throughput can be increased by reducing in-trail landing separation between aircraft, but the consequence may be an increase in the chance of a severe wake vortex encounter or a simultaneous runway occupancy (or go-around). Current instrument flight rule (IFR) standards provide fixed separation minima for given pairs of wake vortex weight classes of aircraft. In practice, the observed separation is a random variable and fluctuates near or above the specified minimum. In this paper, we propose a framework for statistical separation standards that specifies not only a lower bound for the separation but also a standard for the target value and the variance of the process. We address the question of what a more efficient separation standard is in order to control the risk in the approach process. We also consider whether separation variability may be reduced by employing such standards, i.e. more detailed standards that take the "realized variability" into account. Analytical results of this study suggest that (under specific assumptions) throughput can be increased to some extent without degrading safety for the given facilities, infrastructure, and weather condition. The arguments and concepts are illustrated with statistical observations from Detroit airport (DTW)