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 to
counteract effectively in constrained operational
environments such as the flight deck. Left unad-dressed,
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-uneventful
nighttime flights.
Currently there is no system in place to assist
flight crews in managing their alertness. Furthermore,
strategy choices are severely restricted in the flight
deck environment. For example, although previous
research has demonstrated the effectiveness of a
26-minute nap in significantly improving subsequent
physiological alertness and performance, the FAA
does not currently sanction napping on the flight
deck. 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 enroute") with but a few exceptions.
Nevertheless, surveys of flight crews reveal that
many use physical activity as a countermeasure
during fatiguing flights. Despite this widespread belief
by flight crews in the effectiveness of physical
activity, there have been no controlled studies of its
effect on vigilance, sleepiness, and performance in
the aviation environment. This flight simulator study
examined whether regularly spaced brief bouts of
controlled physical activity (standing up, walking,
stretching) combined with social interaction could
improve alertness and performance during a long,
uneventful, overnight flight requiring extended
wakefulness and vigilance. The data obtained from
this study support NASA's Aero-Space Technology
Enterprise and its objective of reducing the aircraft
accident rate.
Fourteen two-man crews flew a 6-hour (2:00-
8:00 a.m.) uneventful flight from Seattle to Honolulu
in the Ames 747-400 flight simulator. The 14 subjects
in the Treatment Group received five short (7-minute)
breaks with controlled physical activity and social
interaction, spaced hourly during the cruise portion
of the flight. An equivalent number in the Control
Group received only one 7-minute break in the
middle of cruise. Measures of psychomotor vigilance
performance, subjective sleepiness, continuous brain
wave activity (electroencephalography; EEG), and
continuous eye movement activity (electrooculography;
EOG) were collected throughout the flight.
Treatment subjects receiving the hourly activity
breaks reported significantly greater subjective
alertness when it was measured at 5, 15, and
25 minutes post-break, with the strongest effects near
the time of the daily circadian trough in alertness
(~5:00-6:30 a.m.). The benefit in subjective alertness
dissipated by 40 minutes post-break, and there was
no evidence of objective vigilance performance
improvement when it was sampled from 15 to
25 minutes post-break. There was the expected
performance deterioration in both groups because of
an elevated sleep drive and the circadian time of day.
However, during the latter part of the night, the EEG
and EOG measures for the Treatment Group revealed
statistically significant post-break reductions relative
to the Control Group in slow eye movements, EEG 12
theta-band activity (two indicators of drowsiness),
and episodes of stage 2 and 3 sleep. The figure shows
that in the sampled 15-minute periods at 5:40 a.m.
and 6:40 a.m., the Control Group pilots were either
asleep (stage 2 or 3) or exhibiting significant sleepiness
(EEG theta activity) 20%-25% of the time.
Conversely, the Treatment Group pilots, who had just
received a 7-minute break, fell asleep or exhibited
significant sleepiness for less than 5% of the time
during the same two periods. Furthermore, higher
numbers of Control subjects exhibited sleepy behaviors
during these two time periods (12 of 14 subjects)
than Treatment subjects (no more than 7 of
13 subjects).
Overall, the physiological data were consistent
with subjective reports in indicating that brief,
controlled activity breaks were effective in reducing
nighttime sleepiness for at least 15 minutes post-break.
The breaks provided particular benefits during
the early morning hours - the circadian time associated
with the greatest vulnerability to fatigue. Furthermore,
the breaks continued to mask any underlying
sleepiness for up to 25 minutes post-break. The
physical activity that occurred as part of the breaks
most likely produced enough sympathetic nervous
system activation to produce an EEG response
characteristic of increased arousal.
Controlled activity breaks are not substitutes for
adequate sleep, but they do represent a practical,
short-term countermeasure to the fatiguing effects of
a long nighttime flight, provided appropriate controls
are in place to ensure the wakefulness and alertness
of the other crewmembers remaining on the flight
deck.
Point of Contact: M. Mallis
(650) 604-3654
mmallis@mail.arc.nasa.gov
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