Free flight and the air traffic controller: Active control versus passive monitoring

Free Flight, as originally proposed by the RTCA (1995), would allow transfer of authority for separation of aircraft from the air traffic controller to the pilot. More recent proposals have called for final authority to rest with the controller (FAA, 1997). These proposals have differing implications for the controller in terms of active control and passive monitoring. The present study investigated the effects of active control versus passive monitoring and traffic density on controller mental workload, performance, and memory in an air traffic control (ATC) task simulating FF conditions. Eighteen ATC specialists participated in an ATC simulation. Independent variables were (1) active control versus monitoring of traffic and (2) moderate versus high traffic density. Dependent variables included accuracy and timeliness in detecting potential conflicts, accepting and handing-off aircraft. Mental workload was assessed with a secondary task, heart rate variability and NASA-TLX ratings. Controller memory of aircraft positions was tested. Results showed detrimental effects of high traffic and passive control on performance. High traffic density increased mental workload. The detrimental effects of passive monitoring on controller performance validate the recent proposal to keep separation authority with the controller.