Scott M. Galster, Jacqueline A. Duley, Anthony J. Masalonis, and Raja Parasuraman The Catholic University of America, Cognitive Science Lab
The rapid growth in worldwide air travel projected for the next decade will dramatically increase demand for air traffic services. As a result, several new strategies for more efficient air traffic management (ATM) have been proposed ( Perry, 1997; Wickens, Mavor, Parasuraman, & McGee, 1998), among them Free Flight (FF). The goal of FF is to allow aircraft under instrument flight rules the ability to choose, in real time, optimum routes, speeds, and altitudes, in a manner similar to the flexibility now given only to aircraft operating under visual flight rules. ( RTCA, 1995). To achieve this goal, traditional strategic-based separation (flight-path based) will be replaced by tactical separation based on flight position and speed. The responsibility for separation will gradually shift from the current ground-based system to a more cooperative mix between the air and ground. FF can be viewed as a series of stages on a continuum, along which new technologies and procedures will be added as they prove useful and effective in the attainment of the mature FF goal.
While relinquishing active responsibility for separation, the air traffic controller (ATCo) will become more of a monitor as FF moves towards a mature level. A recent report by a National Research Council ( NRC) panel on future ATM raised some concerns regarding this development ( Wickens et al., 1998). One concern is how effective a controller can be in a purely monitoring role ( Parasuraman & Riley, 1997). Human monitoring of automated systems can be poor, especially if the operator has little active control over the automated process ( Parasuraman, Molloy, & Singh, 1993). Because of such concerns, the NRC panel recommended that authority for separation remain firmly on the ground, with a greater emphasis being placed on providing automation support tools for ATCos ( Wickens et al., 1998). Nevertheless, the panel recommended that extensive human-in-the-loop simulations be conducted to evaluate different FF concepts for their impact on safety and efficiency. Moreover, no matter what level of FF is eventually implemented, ATCos will remain ultimately responsible for maintenance of safety (ensure separation). As a result, there is an urgent need to investigate the effects of different levels of FF on ATCO workload and performance.
Endsley, Mogford and Stein ( 1997) recently conducted such a study with full performance level (FPL) en-route civilian controllers under four different procedural conditions: current procedures (baseline), direct routing, direct routing allowing pilot deviations with conveyed intent, and direct routing allowing pilot deviations without conveyed intent. ATCos reported significantly higher subjective workload when they were not advised of pilot intentions in advance of a deviation from the flight plan. They also showed a trend towards committing more operational errors in the direct routing without shared intent condition compared to the baseline condition. This trend suggested that controllers found it difficult to maintain separation standards when they did not have a clear picture of the pilot's intentions, as might be the case in mature FF.
Hilburn, Bakker, Pekela, and Parasuraman ( 1997) also examined the impact of FF on the performance of U.K. military controllers. Conventional control in structured airspace was compared to FF conditions in which aircraft did or did not share intent information with controllers. These conditions were crossed with low and high traffic levels. ATCos reported higher subjective mental workload for high traffic loads; however, there were no overall differences between the control conditions. ATCos also reported higher mental workload in high traffic scenarios under conventional control conditions than they did under uninformed FF. Physiological measures of workload, including blink rates and pupil diameter, revealed a