Short-haul Commercial Operations
(Above)Example entry in a pilot's daily logbook.

This study was conducted to examine the extent of sleep loss, circadian disruption and fatigue engendered by flying commercial short-haul air transport operations (flight legs less than eight hours). In this study, 74 pilots from two different airlines were studied before, during, and after 3- and 4-day commercial short-haul trips. All flights took place on the east coast of the United States and occurred throughout the year. Of the pilots contacted about the study, 85% agreed to participate. As a group, the pilots averaged 41.3 years of age and had, on average, 14.6 years of airline experience. Physiological data (core body temperature and heart rate) and motor activity were obtained every two minutes with the Vitalog portable biomedical monitor. Using the Pilot's Daily Logbook, subjects provided subjective ratings of fatigue and mood every two hours while awake, and recorded their sleep episodes and other activities (e.g., meals, exercise, duty time). All subjects completed a background questionnaire and a NASA cockpit observer accompanied crews during trip schedules.

The specific daytime and evening trips studied were selected to provide information about the upper range of fatigue reported by pilots in these operations. Common features of the trip schedules included early report times and multiple flight legs (average 5.5/day) over long duty days. The trips averaged 10.6 hrs of duty per day and involved an average of 4.5 hrs of flight time. One-third of the duty periods studied were longer than 12 hours. The average rest period was 12.5 hrs long and usually occurred progressively earlier in the day across successive trip days. Data from the self-report daily logbook demonstrated that during the trip nights, pilots took longer to fall asleep (about 12 mins longer), slept less (about 1.2 hrs shorter), and awoke earlier (about 1.4 hrs) compared to pre-trip sleep patterns. The pilots reported this trip sleep as lighter and poorer (with more awakenings) compared to pre-trip sleep. Subjective fatigue and mood were worse during layovers compared to levels pre-trip, during flights, or post-trip. Significant time-of-day effects were found for fatigue, negative emotions, and activation ratings. In the first three ratings of the day, fatigue and negative emotion ratings were low following awakening, and increased to reach their highest values in the final rating prior to sleep. Predictably, activation ratings showed the inverse of this pattern.

On trip days, pilots consumed more caffeine (average 3.4 servings) compared to on pretrip days (average 1.9 servings) and on posttrip days (average 2.7 servings), presumably to maintain alertness during operations. These were consumed primarily in the early morning associated with the earlier wakeup and duty times and also, during the mid-afternoon peak in physiological sleepiness. During the trip schedule more alcohol (average 1.6 servings) was consumed compared to pre-trip (average 0.5 servings) and post-trip (average 1.0 servings) days. The additional alcohol consumption can be assumed to have occurred after coming off duty (presumably to "spin down" after a long duty day) and before sleep (and within accordance of Federal Aviation Regulations).

This was one of the first field studies conducted by the NASA program and provides a unique insight into the physiological and subjective effects of flying short-haul commercial operations. It demonstrated that these measures could be obtained in an operational environment without disturbing regular performance of duties. The study results suggest several significant operational considerations regarding fatigue. For example, the data showed that the daily duty durations were double the flight durations and a third of the duty periods were longer than 12 hours. The present Federal Aviation Regulations (FARs) set specific pilot limits based on actual flight times. Findings from this study suggest that limitations on duty time should be considered, just as flight times are currently limited. Also, the practice of earlier duty times on successive trip days, requiring earlier wakeup times, interferes with obtaining adequate sleep. Even when the layovers were relatively long, the circadian system would generally inhibit falling asleep earlier and hence the significant sleep loss during trip nights. Therefore, when possible, duty times across successive trip days should remain constant or begin progressively later (moving with the natural tendency of the biological clock to extend the day).

Finally, alcohol is known to disrupt sleep dramatically and therefore contributes to the poor quantity and quality of sleep obtained on trip nights. Alternative approaches to the use of alcohol to unwind after duty and promote sleep should be identified and offered (e.g., relaxation techniques).