Evaluating the Impact of Passive Fatigue on Pilots Using Performance and Subjective States Measures.

Fatigue is a serious threat to flight safety, being a contributing factor of many aviation accidents. Sleep-related fatigue has been the most researched; however, fatigue also depends on task-related factors such as time-on-task and workload. Desmond and Hancock [ 1 ] theorized two opposite types of task-related fatigue: active fatigue (induced by cognitive overload) and passive fatigue (elicited by prolonged, understimulating and monotonous tasks). Research mainly conducted in the automotive sector demonstrated the existence of these different states and found that passive fatigue is linked to decline in performance and vigilance, together with task disengagement. Automation is extensively used in most flights, and though pilots are particularly vulnerable to passive fatigue due to the nature of their tasks (especially during cruise with autopilot engaged), no specific passive fatigue research involving pilots exist. This study intended to fill that gap, by employing well-rested licensed pilots (N = 26) who underwent an experiment involving the Multi-Attribute Task Battery (MATB) which replicates some of the tasks encountered during flight. Pilots were randomly assigned to either a one-hour very low workload scenario intended to induce passive fatigue, or a one-hour moderate workload control scenario. Pilot performance on the MATB was measured as simple reaction times (SRTs) and the frequency of missed cues on a system-monitoring task. Subjective measures were used to evaluate how task engagement and perceived workload changed over the course of the experiment. Results confirmed that passive fatigue had a detrimental effect on performance as pilots in that scenario showed significantly slower SRTs compared to the control group. Task engagement scores did not decline as predicted, but instead increased significantly more in the passive fatigue scenario, indicating a possible self-assessment inefficacy generated by the monotonous tasks. These findings suggests that wakeful pilots experience performance decline during prolonged monotonous and mostly automated flights, thus a wiser use of automation or the development of appropriate countermeasures is needed.