Human Systems Integration Division @ NASA Ames

Controller workload has been a focal topic in air traffic management research because it is considered a key limiting factor to capacity increase in air traffic operations. Because workload ratings are subjective and highly prone to individual differences, some researchers have tried to replace workload with more objective metrics, such as aircraft count. A significant caveat in substituting these metrics for workload ratings, however, is that their relationships are non-linear. For example, as the number of aircraft increases linearly, the controller's perceived workload jumps from low to high at a certain traffic threshold, resulting in a step- function increase in workload with respect to aircraft count, suggesting that controllers perceive workload categorically. The non-linear relationship between workload and aircraft count has been validated using data collected from a recent study on the En Route Free Maneuvering concept element (Lee, Prevot, Mercer, Smith, & Palmer, 2005). The results suggest that objective metrics, such as aircraft count, may not be used interchangeably with subjective workload. In addition, any estimation on workload should not be extrapolated from a set of workload measures taken from an experiment since the extrapolated workload is likely to significantly underestimate workload.