The Effect of Trajectory-based Operations on Air Traffic Complexity

Airspace capacity is in most part influenced by air traffic controller workload which increases with the increase of air traffic complexity. With transition to trajectory-based operations (TBO), a decrease in air traffic controller workload is expected ; however, the effect on air traffic complexity was not studied. Due to this, it was necessary to measure and compare complexity during conventional operations versus TBO. For this purpose 10 air traffic controllers were recruited to perform a series of real-time human-in-the-loop simulation runs in conventional and trajectory- based operations. Subjective complexity scores were collected in real-time. It was found that the air traffic complexity is reduced in TBO. The reduction in complexity was detectable only at higher fractions of aircraft flying according to TBO (≥70% of aircraft in the fleet mix) and at higher traffic loads (>15 aircraft simultaneously present in the airspace sector). Furthermore, 20 commonly used complexity indicators were tested for correlation with subjective complexity scores and a predictive linear model was produced using six of them. However, regression analysis showed that the commonly used complexity indicators underperform in TBO so it was necessary to define new complexity indicators which are appropriate for analysis of the effect TBO will have on air traffic. Seven novel, TBO-specific, complexity indicators, were developed and experimentally validated. Two of those outperformed a couple of the complexity indicators used in the previous model.