Impact of freeze horizon on the variation of delay distribution and workload for en route metering

In time-based metering operations the freeze horizon is a key parameter with respect to operational efficiency and feasibility. Freeze horizon is the upstream distance/time from the metering fix at which the sequence and scheduled times of arrival for the metered flights are frozen and conformance operations can begin. When delay absorption begins too soon, systemic uncertainties such as internal departure times can result in unnecessary delay. When delay absorption begins too late, controller workload increases, and conformance to the schedule may require excessively large speed and/or turning maneuvers. This paper examines the variation in the distribution of delay and workload as a function of freeze horizon in order to better select efficient and feasible freeze horizons for time-based metering operations. The results indicate that the freeze horizon duration significantly affects the distribution of delay among the sectors. Additionally, the number of delay absorption control actions (e.g., speed and heading changes), which contribute to controller workload, varies with the freeze horizon.