Flight operations often result in fatigue, sleep loss, and circadian disruption leading to significant decrements in alertness and performance. These problems can be difficult to detect reliably and counteract effectively in constrained operational environments. Yet, left unaddressed, alertness and performance decrements reduce the margin of safety and increase the chances of an incident or accident.

One serious challenge facing flight crews is the requirement to maintain vigilance during long, highly-automated, and often boring nighttime flights. There is no system currently in place to assist flight crews in managing their alertness. Furthermore, strategy choices are severely restricted on the flight deck. For example, while a 26-min nap has been demonstrated to result in significant improvements in subsequent physiological alertness and psychomotor performance,¹ napping on the flight deck is not currently sanctioned by the FAA. Current Federal Aviation Regulations also mandate that flight crews remain seated: "…each required flight crewmember on flight deck duty must remain at the assigned duty station with seat belt fastened while the aircraft is taking off or landing, and while it is en route" (FAR requirement).

Nevertheless, surveys of flight crews reveal that many use physical activity as a fatigue countermeasure. Despite this widespread belief by flight crews in its effectiveness, there have been no controlled studies in the aviation environment. The present experiment was designed to test the hypothesis that mild physical activity, coupled with social interaction, would improve alertness and performance during a long, uneventful, overnight flight requiring extended wakefulness.

•Evaluate physical activity combined with social interaction as a countermeasure to the fatiguing effects of a long nighttime flight.

•Level D 747-400 flight simulator with 2-man crews (29-62 yrs)

•6-hr, uneventful, transoceanic, nighttime flight (0200-0800), encompassing the time of the circadian trough

•Experimental Group (n=14)
-Five short (7-min) breaks with physical activity, spaced hourly during cruise

•Control Group (n=14)
-One 7-min break only, in middle of cruise portion of flight

•Measures
-Psychomotor vigilance performance task (PVT; 10-min)
-Karolinska Sleepiness Scale (KSS)
-Visual Analogue Sleepiness Scale (VAS)
-Continuous EEG/EOG
-Continuous video of the face (not reported here)

Fig. 1. Photos of Captain (left) and First Officer (right) completing KSS and PVT, respectively, on the flight deck of the 747-400 simulator. Subjects are also instrumented for collection of brain wave (EEG) and eye movement (EOG) measures.

KSS: Karolinska Sleepiness Scale
VAS: Visual Analogue Scale
PVT: Psychomotor Vigilance Task

Fig. 2. Snapshot of first hr of protocol (out of 5 hrs during cruise) for Treatment group. Control group received a break during middle hour of cruise only

•No differences between groups preflight, as expected

•Control Group
-Circadian-mediated increase in sleepiness during night

•Treatment Group
-Sleepiness pattern significantly and positively affected by breaks
-Significantly less subjective sleepiness than Controls, especially in latter part of night (near circadian trough) when sleepiness is greatest
-Effect present at 5-min post-break (KSS), 15-min post-break (VAS) and 25-min post-break (VAS) but disappears by 40-min post-break
(KSS)

Fig. 3. Karolinska Sleepiness Scale. First three measures were pre-flight. Subsequent measures were obtained 5-min and 40-min post-break. Last measure was post-flight. Dashed lines indicate timing of activity breaks. Control group received middle break only. TOC = top of climb. Asterisks indicate significant Treatment vs. Control differences (*p<.05, **p<.01, ***p<.001).

Fig. 4. Visual Analogue Scale. First six measures were pre-flight. Subsequent measures were obtained 15-min and 25-min post-break. Last two measures were post-flight. Remaining features are the same as in Fig. 3.

•No differences between groups preflight, as expected

•No significant differences between Treatment and Control groups during cruise portion of flight

•Circadian-mediated increase in median RT during the night for both groups

•Expected increase in RT variability for both groups during the second half of night when sleepiness is greatest

•Other PVT measures (e.g., lapse frequency) show similar pattern

•Failure to replicate subjective sleepiness effects could indicate either performance task is insensitive or the breaks might only be "masking" sleepiness

•Less physiological sleepiness in Treatment group during 15-min post-break interval than in Control group during a corresponding time interval

•Effect most pronounced during the time of the circadian trough

•Greater percentage of slow eye movements in Controls (Fig. 6)

•Greater percentage of theta activity in Controls (Fig. 7)

•Trend toward increased sleep (stages 2&3) in Controls (Fig. 8)

Fig. 6. Mean percentage (+1 sem) of visually scored slow eye movements (³ 4 sec) during the 15-min post-break periods (corresponding time periods for Controls), excluding the post-middle-break also received by the Controls.

Fig. 7. Mean percentage (+1 sem) of visually scored theta activity during the 15-min post-break periods (corresponding time periods for Controls), excluding the post-middle-break also received by the Controls.

•Flight crews receiving brief hourly activity breaks report significantly greater alertness for up to 25 min
-Effect strongest near the time of the circadian trough

•No evidence of objective vigilance performance improvement by 15-25 min post-break
-Expected performance deterioration occurred due to elevated sleep drive and circadian time

•Alertness & performance data consistent with earlier study showing trend of reduced sleepiness for 10-15 min after light exercise but no effect on auditory vigilance performance.²

•EEG/EOG data are consistent with subjective data in indicating brief activity breaks do reduce nighttime sleepiness for at least 15-min
-Breaks may continue to "mask" sleepiness for up to 25-min

Brief, hourly in-flight activity breaks:

•Reduce subjective sleepiness during circadian trough

•Reduce physiological sleepiness for at least 15 min during circadian trough

•Fail to show an effect on performance 15-25 min post-break

•Are valued by flight crews, practical, and operationally feasible