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Flight operations can involve rapid multiple time changes and long, irregular work schedules. These factors can result in sleep loss, circadian disruption, and fatigue with subsequent effects on flightdeck performance. Countermeasures to reduce or mitigate the effects of these factors can be divided into two approaches: preventive strategies and operational countermeasures. Preventive strategies are used prior to a duty period to reduce or mitigate the fatigue created by flight and duty schedules. Operational countermeasures are used during flight operations to maintain performance and alertness. Naps can be used as both a preventive strategy and an operational countermeasure. Strategic napping in two different flight operation environments will be used to illustrate its application as a fatigue countermeasure. A recent NASA/FAA study examining the effectiveness of a preplanned cockpit nap to acutely improve alertness and performance on the flightdeck will be described.

Work-rest schedules during long duration space missions involve several factors which could disrupt sleep and circadian temporal organization: 1) substantial displacement of sleep with respect to mission control time, due to two-shift operations; 2) schedule changes, either planned or in response to unforeseen operational events; 3) social and light zeitgebers substantially different from those on earth; 4) pulses of hypergravity associated with launch and re-entry, and prolonged exposure to microgravity. Timed bright light exposures have recently received much attention as a possible countermeasure to accelerate adaptation to schedule changes. Four male subjects were therefore exposed to two sessions of eleven days of simulated weightlessness (6° head-down tilt bedrest) with six hour extensions of the scheduled waketime on days 3 and 4 (12 h phase delay).