The Role of the Air Traffic Controller in Future Air Traffic Management: An Empirical Study of Active Control versus Passive Monitoring

Metzger, Ulla; Parasuraman, Raja · 2001 · OpenAlex-citations

DOI: 10.1518/001872001775870421

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Summary

This study investigates the impact of future Air Traffic Management (ATM) concepts, specifically "Free Flight" (FF), on air traffic controller (ATCo) performance. FF proposals suggest transferring separation responsibility from ATCos to pilots, shifting the controller’s role from active control to passive monitoring. The research addresses the critical question of whether this shift compromises safety, particularly regarding conflict detection, mental workload, and situational awareness under high traffic densities. The authors conducted an empirical simulation study involving 14 active ATCos. Participants engaged in a 2x2 within-subject design comparing active control versus passive monitoring under moderate (11 aircraft) and high (17 aircraft) traffic densities. In the active condition, ATCos issued clearances to resolve conflicts; in the passive condition, they only monitored traffic and acknowledged potential conflicts. Performance metrics included the accuracy and timeliness of conflict detection, aircraft hand-off efficiency, memory for aircraft location, and mental workload assessed via secondary tasks, heart rate variability, and subjective ratings. Results indicated that high traffic density significantly degraded performance across all conditions, with ATCos missing 65.18% of potential conflicts compared to 14.73% under moderate traffic. Crucially, passive monitoring imposed a significant performance penalty under high traffic. While the rate of missed conflicts did not differ significantly between control types, ATCos detected conflicts nearly two minutes later under passive monitoring than under active control in high-density scenarios. Additionally, ATCos demonstrated poorer memory for aircraft altitudes under passive monitoring (6.25% recall) compared to active control (16.67% recall). Mental workload, measured subjectively and via secondary task performance, increased significantly with traffic density but showed no significant difference between active and passive control conditions. The findings suggest that removing decision-making authority from ATCos leads to an "out-of-the-loop" phenomenon, severely impairing their ability to detect conflicts quickly and maintain situational awareness. The study concludes that the detrimental effects of passive monitoring, particularly under the high traffic densities envisioned for future ATM, support proposals to retain separation authority with ground-based controllers. The authors argue that active control, potentially supported by automation aids, is safer and more effective than the passive monitoring role proposed in early Free Flight concepts.

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