A regularly scheduled 12 day, 8 leg trip schedule that involved multiple transpacific crossings was chosen. The flight lengths averaged just over 9 hrs followed by about 25 hrs of layover. Prior to, during, and after the 12 day trip schedule, crew members completed Pilot Daily Logbooks documenting sleep and duty times and other activities and wore actigraphs on their nondominant wrist. The middle 4 legs of the trip schedule were studied intensively. Measures during the study flight legs included continuous physiological monitoring of EEG (brain) and EOG (eye movement) activity using a Medilog recorder. An extensive scientific literature demonstrates that self-reports of sleep (e.g., time to fall asleep, total sleep time) do not accurately reflect physiological activity. Therefore, it was critical to document the amount of physiological sleep obtained. The continuous EEG and EOG recordings during the wakefulness period were also used to assess physiological sleepiness. The Psychomotor Vigilance Task (PVT) was used as a measure of vigilance performance/sustained attention. Pilots also gave self-report ratings of alertness and mood at predetermined times throughout the flight. Two NASA researchers traveled with the crews to implement the procedures and collect data. The 3-person B747 volunteer crew members were randomly assigned to either a Rest Group or No-Rest Group. Each Rest Group crew member (12 Subjects) had a 40-min rest opportunity during the cruise, low workload portion of flights over water. Crew members rested one at a time on a prearranged rotation while the other two crew members maintained the flight. The No-Rest Group crew members (9 Subjects) had a 40-min control period identified when they were instructed to continue their regular flight activities. Specific safety and procedural guidelines were used during the study.

The first question was whether pilots would be able to sleep given a planned rest opportunity in their cockpit seat. The Rest Group crew members slept on 93% of the rest opportunities. On average, they fell asleep in 5.6 mins and slept for about 26 mins. If pilots were able to nap, it was also critical to determine whether there was a benefit associated with this sleep. This was determined by examining the vigilance performance measure and indicators of physiological sleepiness. As expected, the No-Rest Control Group showed performance decrements at the end of flights compared to the beginning of flights, on night flights versus day flights, and on the fourth study leg compared to the first study leg. However, the positive effects of the brief nap were demonstrated in the Rest Group as they maintained consistently good performance at the end of flights, on night flights, and on the fourth study leg. The naps were associated with the subsequent maintenance of initial performance levels compared to the decrements observed in the No-Rest Group. Physiological sleepiness was examined by evaluating the subtle EEG and EOG changes that occur indicating state lability. Previous research has demonstrated that physiological sleepiness is associated with the occurrence of EEG alpha or theta and/or EOG slow eye movements. These physiological events are associated with decreased performance. Microevents indicative of physiological sleepiness (the occurrence of EEG alpha or theta and/or EOG slow eye movements), lasting 5 secs or longer, were identified during the last 90 mins of flight, including descent and landing, for both study groups. Overall, the No-Rest Group had microevents (average of 6.37) indicative of physiological sleepiness at a rate twice that of the Rest Group (average of 2.90 microevents).

This brief "NASA nap" appeared to act as an acute inflight operational safety valve and did not affect the cumulative sleep debt observed in 85% of the crew members. The Rest Group crew members were able to obtain sleep during the rest opportunity and this nap was associated with improved performance and alertness compared to the No-Rest Control Group. This was the first empirical test of a fatigue countermeasure conducted in an operational aviation setting that combined physiological, performance, and subjective measures.

Again, not only are the results scientifically interesting but they can be transferred directly into operational considerations regarding planned rest. Based partly on the results of this NASA/FAA study, an industry/government working group has drafted an Advisory Circular (AC) for Controlled Rest on the Flight Deck. The AC outlines specific guidelines for the development and implementation of a program for controlled rest on the flight deck. It should be noted that controlled rest is only one acute inflight countermeasure and is not the panacea for all of the sleep loss and circadian disruption engendered by long-haul flight operations.

NASA_TM_94_108839.pdf (6.6 MB for the full report)

Operational Summary.pdf (554K)

Intro.pdf (405K)

Methods.pdf (1 MB)

Results.pdf (2.8 MB)

Discussion.pdf (962K)

Reference and Appendix.pdf (601K)

Last Update: April 24, 2000