Analysis of the excess Inter-Arrival Time distribution

A critical element in relieving airport capacity constraints is to minimize longitudinal spacing between aircraft pairs that are in-trail on final approach. The Federal Aviation Administration (FAA) has defined minimum separation standards that controllers need to follow when directing arrivals during instrument meteorological conditions. Excess Inter-Arrival Time (IAT) between arrivals may occur in addition to the FAA minimum separation standards. This excess time could be due to a number of factors including speed variations between the two aircraft in the arrival pair, pilot techniques, wind speeds and conservative air traffic management. The spacing and distribution of excess IAT between aircraft in instrument approach conditions is an important factor when modeling airport capacities. Current best practices for modeling the distribution of excess IAT is based on 35-year old research. Evaluating these modeling assumptions has been difficult due to a lack of sufficient, reliable data. The recent advent of new tools and the explosion of new, highly accurate data enable a reevaluation of the excess IAT distribution assumptions. This analysis studied 21,752 arrival pairs at seven Traffic Management Advisor-equipped airports. We found that a Log-Normal distribution with a log-mean of 4.27 seconds, a log-standard deviation of 0.25 seconds and shifted by 50 seconds provides a better fit to the observations than the Normal distribution that was previously assumed.