Recent free flight proposals to relax airspace constraints and give greater autonomy to aircraft have raised concerns about their impact on controller performance. Relaxing route and altitude restrictions would reduce the regularity of traffic through individual sectors, possibly impairing controller situation awareness. This study examined the impact of reduced regularity of traffic in four visual search experiments that tested air traffic controllers' detection of traffic conflicts in the four conditions created by factorial manipulation of fixed routes (present versus absent) and altitude restrictions (present versus absent). These four conditions were tested under varying levels of traffic load and conflict geometry (conflict time and angle). Traffic load and conflict geometry showed strong and consistent effects in all experiments. Color coding altitude also significantly improved detection times. In contrast, removing altitude restrictions had only a small negative impact, and removing route restrictions had virtually no negative impact. In some cases, conflict detection was actually better without fixed routes. The implications and limitations of the results for the feasibility of free flight are discussed.
Abstract