Rosekind, M. R., Co, E. L., Johnson, J. M., Smith, R. M., Weldon, K. J., Miller, D. L., Gregory, K. B., Gander, P. H., Lebacqz, J. V. (1994). Alertness Management in Long-Haul Flight Operations. Proceedings of the 39th Annual Corporate Aviation Safety Seminar (pp. 167-178). St. Louis, Missouri: Flight Safety Foundation.
"My mind clicks on and off . . . I try letting one eyelid close
at a time while I prop the other open with my will. But the effort's too
much. Sleep is winning. My whole body argues dully that nothing, nothing
life can attain, is quite so desirable as sleep. My mind is losing resolution
and control."
Fatigue has been an issue in long-haul flight operations since the first transoceanic crossing by Charles Lindbergh. Today, modern aircraft have the capability to fly farther, are more highly automated, and require fewer flight crewmembers for operation. While aircraft and the operational demands of a global aviation industry have evolved, human requirements for sleep have not. Therefore, the physiological capabilities and limitations of the human operator remain central to maintaining the safety margin in long-haul flight operations. This paper will address some of the physiological mechanisms that underlie fatigue, highlight findings regarding fatigue in long-haul operations, and suggest some alertness management strategies.
Physiological Mechanisms that Underlie Fatigue
Since the mid-1950s, there has been extensive scientific research on sleep, sleepiness, circadian rhythms, sleep disorders, dreams, and the effects of these factors on waking alertness and human performance (e.g., see refs. 1 and 2). Some of the basic scientific findings regarding human sleep, sleepiness, and circadian rhythms that have emerged over the past forty years are critical to understanding the physiological mechanisms that underlie fatigue in flight operations. Some of the significant information is presented as a foundation for understanding the role of fatigue in long-haul operations (ref. 3).
Sleep is a Vital human Physiological Function. Historically, sleep has been viewed as a state when the human organism is turned off. Scientific findings have clearly established that sleep is a complex, active physiological state that is essential to human survival. Like human requirements for food and water, sleep is a vital physiological need. When an individual is deprived of food and water, the brain provides specific signals-hunger and thirst-to drive the individual to meet these basic physiological needs. Similarly, when deprived of sleep, the physiological response is sleepiness. Sleepiness is the brain's signal to prompt an individual to obtain sleep; it is a signal that a specific physiological require-ment has not been met. Eventually, when deprived of sleep (acutely or chronically), the human brain can spontaneously, in an uncontrolled fashion, shift from wakefulness to sleep, in order to meet its physiological need for sleep. The sleepier the person, the more rapid and frequent are these intrusions of sleep into wakefulness. These spontaneous sleep episodes can be very short (i.e., microsleeps lasting only seconds) or extended (i.e., lasting minutes). At the onset of sleep, an individual disengages perceptually from the external environment, becoming unresponsive to outside information. Therefore, even a micro-sleep can be associated with a significant performance lapse when an individual does not receive or respond to external information. With sleep loss, these uncontrolled sleep episodes can occur while standing, operating machinery, and even in situations that would put an individual at risk, such as driving a car (refs. 4-6).
How much sleep does an individual need? An individual requires the amount of sleep necessary to achieve full alertness and the highest level of functioning during waking hours. There is a range of individual sleep needs and, though most adults will require about 8 hours of sleep, some people need 6 hours while others require 10 hours to feel wide awake and function at their peak level during wakefulness.
Sleepiness Affects Waking Performance, Vigilance, and Mood. Sleep loss creates sleepiness and often this sleepiness is dismissed as a minimal nuisance or as easily overcome. However, sleepiness can potentially degrade most aspects of human capability. Controlled laboratory experiments have demonstrated decrements in most components of human performance, vigilance, and mood as a result of sleep loss. Sleepiness can be associated with decrements in decision-making, vigilance, reaction time, memory, psychomotor coordination, and information processing. Research has demonstrated that with increased sleepiness, individuals demonstrate degraded perform-ance despite increased effort, and report an indifference regarding the outcome of their performance. Individuals report fewer positive emotions, more negative emotions, and an overall worsened mood with sleep loss and sleepiness (for scientific reviews of this area, see refs. 7-10).
Generally, sleepiness can degrade most aspects of human waking performance, vigilance, and mood. In the most severe instances, an individual may experience an uncontrolled sleep episode and obviously be unable to perform. However, in many other situations, while the individual may not actually fall asleep, the level of sleepiness can still significantly degrade human performance. For example, the individual may react slowly to information, may incorrectly process the importance of the information, may find decision making difficult, may make poor decisions, or may have to check and recheck information or activities due to memory difficulties. This performance degrada-tion can be a direct result of sleep loss and the associated sleepiness and can play an insidious role in the occurrence of an operational incident or accident (refs. 11-13).
Sleep Loss Accumulates into a Sleep Debt. An individual who requires 8 hours of sleep and obtains only 6 hours is essentially sleep deprived by 2 hours. If the individual sleeps only 6 hours over four nights, then the 2 hours of sleep loss per night would accumulate into an 8-hour sleep debt. Estimates suggest that in the United States today, most adults obtain 1 to 1.5 hours less sleep per night than they actually need (ref. 14). During a regular work week this would translate into the accumulation of a 5- to 7.5-hour sleep debt going into the weekend; hence, the common phenomenon of sleeping late on weekends to compensate for the sleep debt accumulated during the week. Generally, recuperation from a sleep debt involves obtaining deeper sleep over two to three nights. Obtaining deeper sleep appears to be a physiological priority over a significant increase in the total hours of sleep. In other words, rather than sleeping 7.5 hours longer than normal on the weekend to "make-up" for the sleep debt accumulated during the week, the sleep-deprived person may sleep only slightly longer than normal in a deeper sleep.
Physiological vs. Subjective Sleepiness. Sleepiness can be differentiated into two distinct components: physiological and subjective. Physiological sleepiness is the result of sleep loss: lose sleep, get sleepy. An accumulated sleep debt will be accompanied by physiological sleepiness that will drive an individual to sleep in order to meet the individual's physiological need. Subjective sleepiness is an individual's introspective self-report regarding the individual's level of sleepiness (refs. 4 and 15). An individual's subjective report of sleepiness can be affected by many factors, for example, caffeine, physical activity, and a particularly stimulating environment (e.g., an interesting conversation). However, an individual will typically report being more alert because of these factors. These factors can mask or conceal an individual's level of physiological sleepiness. Therefore, the tendency will be for individuals to subjectively rate themselves as more alert than they may be physiologically. This discrepancy between subjective sleepiness and physiological sleepiness can be operationally significant. An individual might report a low level of sleepiness (i.e., high level of alertness) but be carrying an accumulated sleep debt with a high level of physiological sleepiness. This individual, in an environment stripped of factors that conceal the underlying physiological sleepiness, would be susceptible to the occurrence of spontaneous, uncontrolled sleep and the performance decrements associated with sleep loss (refs. 16-18).
The Circadian Clock. Humans, like other living organisms, have a circadian (circa=around, dia=a day) clock in the brain that regulates physiological and behavioral functions on a 24-hour basis. In a 24-hour period this clock will regulate our sleep/wake pattern, body temperature, hormones, performance, mood, digestion, and many other human functions. For example, on a regular 24-hour schedule we are programmed for periods of wakefulness and sleep, high and low body temperature, high and low digestive activity, increased and decreased performance capability, and so on. An individual's circadian clock might be programmed to sleep at midnight, awaken at 8 AM, maintain wakefulness during the day (with an afternoon sleepiness period), and then repeat the 24-hour pattern. The circadian rhythm of body temperature is programmed for the lowest temperature between 3 and 5 AM on a daily basis (ref. 19).
When the circadian clock is moved to a new work/rest (or sleep/wake) schedule or put in a new environmental time zone, it does not adjust immediately. This is the basis for the circadian disruption associated with jet lag. Once the circadian clock is moved to a new schedule or time zone, it can begin to adjust and may take from several days up to several weeks to physiologically adapt to the new environmental time. Also, the body's internal physiological rhythms do not all adjust at the same rate, and therefore may be out of synch with each other for an extended period of time. Again, it can take from days to weeks for all of the internal rhythms to come together in a synchronous 24-hour rhythm in the new schedule or time zone.
There are some specific factors that can affect the circadian clock's adaptation. Day/night reversal can confuse the clock so that the cues that help it adjust and maintain its usual physiological pattern are disrupted. Moving from a day to a night schedule and back to days can keep the clock in a continuous state of readjustment, depending on the time between schedule changes. For example, severe effects would accompany a 12-hour day to night to day schedule alteration. Another factor is crossing multiple time zones. While there is some flexibility for adjustment, putting the circadian clock in a time zone three or more hours off home time will require a reasonable amount of physiological adaptation. Another factor can be the direction the clock is moved. Shortening the period (e.g., moving to a 21-hour cycle or day) is generally more difficult than lengthen-ing the period (e.g., moving to 25 or more hours), which is the natural rhythm of the circadian clock. Therefore, it can be more difficult to cross time zones in an eastward direction compared to westward movement. It can also be more difficult to move a work/rest schedule backwards over the 24-hour day compared to moving it forward (e.g., forward from day to swing to night shift). All of the associated difficulties of moving the clock, such as poor sleep, sleepiness, effects on performance, and so on, will be affected until the circadian clock physiologically adapts to the new schedule or time zone (refs. 20 and 21).
Scientific studies have revealed that there are two periods of maximal sleepiness during a usual 24-hour day. One occurs at night roughly between 3 and 5 AM, and the other in midday roughly between 3 and 5 PM. However, performance and alertness can be affected throughout a 12 AM to 8 AM window. Individuals on a regular day/night schedule will typically sleep through the 3-5 AM window of sleepiness. The afternoon sleepiness period can be masked by factors described previously, or present a window when individuals are particularly vulnerable to the effects of sleepiness. This also means that individuals working through the night are maintaining wakefulness from 3-5 AM when their circadian clock is programmed for sleep. Conversely, individuals sleeping during the day are attempting to sleep when the circadian clock is programmed for wakefulness. However, individuals searching for specific windows when they are physiologically prepared to sleep, either for an extended sleep period or a strategic nap, can use these periods to their advantage (ref. 4).
Interaction Between Sleep and Circadian Processes. At any given time, an individual's propensity to sleep or, conversely, the ability to maintain alertness and vigilance, will be the result of an interaction between sleep and circadian processes. An individual's ability to fall asleep quickly and obtain a good quantity and quality of sleep can be related to the prior amount of sleep (i.e., sleep debt) and circadian time of day. An individual with no sleep debt attempting to sleep at a time of circadian wakefulness and alertness will have difficulty falling and staying asleep. However, an individual with a sleep debt attempting to sleep at a time of maximal circadian sleepiness will fall asleep quickly and easily maintain sleep. Also, an individual with a substantial sleep debt may be physiologically sleepy enough to override circadian factors and be able to fall asleep at a circadian time for wakefulness.
These two factors also interact to determine an individual's level of physiological alertness and performance during waking hours. A third factor can also be a consideration: the number of hours of continuous wakefulness. An individual with a sleep debt, awake continuously for 20 hours, and working through the 3-5 AM circadian period of maximal sleepiness will have difficulty maintaining alertness and performance. However, an individual who has obtained the required amount of sleep, has been awake for 10 hours, and is working through the 3-5 AM circadian low will probably have less difficulty maintaining wakefulness. Any one of these three factors can increase an individual's vulnerability for a performance decrement. Two or three of the factors coinciding will increase the probability of a fatigue-related performance problem.
Individual Differences. It is critical to note that there are tremendous individual differences in these physiological factors. There is a range of sleep needs, differences in physiological flexibility for adaptation of the circadian clock, and ability to tolerate sleep loss or circadian disruption. Therefore, while these fundamental properties of sleep and circadian processes are factors for all human physiology, there is a range of individual responses for any particular set of circumstances or operational demands.
Fatigue in long-haul flight operations
In response to a Congressional request, the NASA Ames Fatigue/Jet Lag Program was initiated in 1980 by Dr. John Lauber (currently a member of the National Transpor-tation Safety Board) and Dr. Charles Billings (former NASA Ames Chief Scientist, distinguished aerospace researcher and flight surgeon). The Fatigue/Jet Lag Program has been the beneficiary of a distinguished group of contributors over the years (e.g., Drs. Clay Foushee, Curt Graeber, Bill Reynard, Don Hudson, Ms. Linda Connell, and many others). In 1991, the Program evolved into the NASA Ames Fatigue Countermeasures Program to highlight an emphasis on the development and evaluation of countermeasures (refs. 22 and 23). The original goals of the Program have been maintained; they are:
1) to determine the extent of fatigue, sleep loss, and circadian disruption in flight operations,
2) determine how these physiological factors affect flight crew performance, and
3) develop and evaluate countermeasures to mitigate adverse effects and maximize flight crew performance and alertness during operations.
The NASA Ames Fatigue Countermeasures Program integrates a variety of research methodologies, including data collected during regular flight operations, in full-mission high-fidelity simulations, and in controlled laboratory studies. Over the years, a variety of experimental measures have been used. These measures now include self-report sleep/wake and duty logbooks, physiological variables such as core body temper-ature, continuous brain, eye, and muscle activity, vigilance performance, and actigraphy. The specific measures used have been dependent on the particular objectives in any given study. Since 1980, fatigue has been examined in a variety of flight environments, including short-haul, long-haul, overnight cargo, and helicopter operations (refs. 24-27). These studies have involved both commercial and military flight operations and have been complemented by other ground-based activities. Two specific long-haul studies will be described to demonstrate how the physiological factors (sleep and circadian processes) are expressed in aviation operations.
Long-Haul Field Study. This study combined data from four international trip schedules to examine how long-haul flight crews organized their sleep/wake patterns (ref. 25). Specifically, the study examined how the timing, quantity, and quality of sleep was affected by duty requirements, local time, and the circadian system. The data were obtained from twenty-nine male flight crewmembers (average age 52 years) flying B747 aircraft on commercial international trip patterns. A variety of measures were obtained through-out the trip schedules. Self-report information about duty times, sleep timing, duration, quality, and so on, were collected with a Pilot Daily Logbook. This paper and pencil logbook fit easily into a pocket or flight bag and was completed from several days prior, to several days following the trip schedule. Physiological measures included core body temperature and heart rate recorded with the Vitalog portable biomedical monitor. Core body temperature, measured with a rectal thermister, was used as a circadian marker. Physiological data were collected in 2-minute samples and obtained prior to, during, and following the trip schedule.
These self-report and physiological measures provided informative results about the duty periods, sleep/wake patterns, and underlying circadian time-keeping system. The average, basic duty/rest pattern that emerged was 10.3-hour duty periods followed by 24.8-hour layovers. An examination of the overall sleep/wakefulness pattern demon-strated the following: 19 hours awake, 5.7 hours sleep, 7.4 hours awake, and 5.8 hours sleep. This pattern revealed that usually there were 2 sleep episodes during layovers. Generally, crewmembers rated the first sleep episode as a better quality and deeper sleep, with an easier sleep onset. The longer the sleep episode, the higher the quality of sleep reported. The circadian system affected the timing and duration of the first layover sleep episode more than the second. Generally, the circadian influence created a preference for sleeping during local night and/or for waking up after the temperature low point. However, a high accumulated sleep debt obtained from eastward flights crossing five or more time zones altered this pattern. In these cases, the sleep debt could override the circadian influences. The timing of the second sleep episode was closely related to the amount of sleep already obtained during layover. This sleep episode usually occurred during local night time and its length was dependent on the time available prior to reporting for duty. When crewmembers fell asleep before the low point of their circadian temperature cycle, the sleep episode durations were longer.
Crewmembers reported naps in their Pilot Daily Logbooks. Results showed that a nap reported as the first sleep episode of a layover averaged about 2 hours and was usually longer than other naps. These first naps generally occurred after periods of longer contin-uous wakefulness-after overnight eastward flights or westward flights that crossed 5 or more time zones. The length of continuous wakefulness was decreased by another pattern that involved naps obtained just prior to the onset of duty. Crewmembers also reported nap episodes on the flight deck. (Current Federal Aviation Regulations do not specifically sanction in-flight cockpit rest periods.) The crewmembers who reported flight-deck naps averaged 46 minutes (ranging from 10 to 130 minutes). Combined data sources suggest that 11% of flight crewmembers took the opportunity to nap when conditions permitted. These self-report and observational data do not allow a distinction between planned rest and the occurrence of spontaneous episodes in response to the sleep loss and circadian disruption engendered by long-haul flight operations.
Overall, the circadian system pushed the sleep/wake cycle into a 25.7-hour period (day), longer than its usual 24-hour period. However, the sleep/wake and circadian systems did become completely uncoupled. The circadian system was unable to quickly adapt to rapid, multiple time zone changes but continued to affect the timing and duration of the sleep episodes. In long-haul commercial flight operations, there will be preferred sleep times determined by physiological and environmental factors. However, these times may not coincide with the scheduled off-duty time and therefore, may restrict the actual time available for sleep.
International Cooperative Layover Study. This project was coordinated by NASA Ames and involved an international group of collaborators from the Institute for Aviation Medicine (United Kingdom), the DLR (Germany), Japan Airlines (Japan), and Stanford University Medical School (United States). Experienced international flight crews were studied to examine the quantity and quality of sleep obtained following multiple time-zone shifts and the effects on subsequent waking levels of sleepiness (ref. 28). Flight crews were studied in sleep laboratories around the world (in collaborators' facilities) after westward and eastward international flights. The laboratory studies involved physiological measurements of standardized sleep/wake variables and during the day, the objective assessment of physiological sleepiness.
The results demonstrated that flight crews usually obtained adequate sleep during layovers by using one of two strategies. They either slept efficiently at selected times or slept less efficiently but stayed in bed longer than usual to increase their total sleep time. The results also provided data to confirm the expected differences in traveling east vs. west. Eastward travel requires decreasing the period of the circadian clock and opposes the clock's natural tendencies. Conversely, westward travel involves lengthening the period of the circadian clock (which is the natural tendency of the clock). Overall, flight crews had slightly worse sleep on layovers compared to sleep at home. However, layover sleep episodes were worse following eastward transitions compared to westward travel. The decreased quantity and quality of sleep obtained after eastward travel was associated with subsequent increases in daytime physiological sleepiness.
Alertness Management Strategies
There is no quick fix or magic bullet to address all of fatigue engendered by long-haul flight operations. Unfortunately, there is no simple solution that will address all individuals, all operational demands, and all the technology currently involved in the aviation industry. Aviation requires 24-hour operations, and a challenge facing the industry is how to incorporate the scientific and physiological knowledge that currently exists into areas that will maintain the safety margin. Therefore, every arena where the knowledge can be applied should be examined for potential improvements.
Four general categories for examination include hours of service, scheduling, design and technology, and personal strategies. Hours of service are affected by both federal regulatory policies and contractual agreements. Scheduling is dictated by a complex variety of factors that are often idiosyncratic to a particular airline's operation. The automation evolution has brought tremendous advances to aviation, though its effects in a variety of domains remain unclear. There is also a variety of personal strategies that can be used to apply the current state of knowledge on a daily basis for flight crews. Each one of these areas should be examined for mechanisms by which to incorporate scientific and physiological information about fatigue. The challenge is to minimize the adverse effects of any particular category and, wherever possible, use each one to maximize alertness and performance during flight operations.
Personal Strategies. We have proposed differentiating alertness management strategies into two components: preventive strategies and operational strategies (ref. 29). Preventive strategies are used prior to duty or on layover to minimize the adverse effects of the underlying physiological factors (i.e., sleep loss and circadian disruption). These strategies include obtaining maximal quantity and quality of sleep prior to duty, scheduling sleep periods during layover, accounting for fatigue factors during trip scheduling, napping, maintaining good sleep habits, exercising, maintaining balanced nutrition, and others. Operational countermeasures are used in flight to maintain alertness and performance during operations. Generally, these strategies may be more short-acting and serve to mask or conceal underlying physiological sleepiness. These counter-measures include physical activity, strategic caffeine use, and social interactions.
As previously described, the only mechanism to reverse a physiological sleep need is sleep. With sleep loss, the brain will signal its need to obtain sleep (i.e., sleepiness) and if necessary, it will shut down to meet this vital physiological need. Anecdotal, observa-tional, and subjective logbook data indicate that long-haul operations can involve the occurrence of spontaneous and uncontrolled sleep episodes. A NASA/FAA study was conducted to determine the effectiveness of a planned cockpit rest period to maintain and/or improve subsequent alertness and performance during long-haul flight operations (ref. 30).
The planned cockpit rest study involved regularly scheduled, three-person, non-augmented, commercial B747-200 transpacific flights. The middle four legs of an eight-leg, twelve-day trip schedule were studied. The study legs involved two day flights and two night flights, and two eastward and two westward flights. Each flight was about 9 hours in length followed by an average layover of 24 hours. Volunteer flight crew-members were randomly assigned to one of two groups. The twelve Rest Group crew-members were each allowed a scheduled 40-minute rest opportunity, one at a time, during the low workload, cruise portion of flight. The rest periods were taken in their seats. The nine No-Rest Group crewmembers each had a 40-minute control period identified, but were instructed to continue their usual flight activities during this period.
Before, during, and after the twelve-day trip schedule, flight crewmembers completed the Pilot Daily Logbook. This provided self-reported information about duty periods, sleep periods, fatigue ratings, and so on. Each crewmember also wore an actigraph, a small wristwatch-size device, that provides objective information about an individual's 24-hour rest/activity cycle. During the four study trip legs, flight crewmembers' brain and eye movement activities were monitored to physiologically determine sleep during the rest opportunity and to evaluate subsequent alertness. Crewmembers were also evaluated with a vigilance performance test and reported their levels of alertness and mood. Crewmembers in both groups were evaluated with exactly the same measures and procedures.
The first question was, "When given the opportunity, would flight crewmembers sleep during the 40-minute rest period?" On 93% of the sleep opportunities, Rest Group crewmembers slept. On average, they fell asleep in 5.6 minutes and slept for 25.8 minutes. The next question was whether this nap was associated with a subsequent maintenance or improvement in alertness and performance compared to the No-Rest Group. The Rest Group maintained consistent vigilance performance on night flights, at the end of a flight leg, and after four consecutive flight legs; the No-Rest Group showed decrements. Also, physiological alertness was examined by analyzing the subtle brain and eye movement changes that indicate sleepiness. The final 90 minutes of flight (about 60 minutes prior to top of descent, through descent and landing) was analyzed for the occurrence of physiological microevents, lasting 5 seconds or longer, which are indicative of decreased alertness. These physiological microevents are similar to "microsleeps" that many individuals have experienced when fighting sleepiness and attempting to maintain wakefulness. The nine No-Rest Group crewmembers had twice as many microevents, including twenty-two during descent and landing, than the twelve Rest Group crewmembers, who experienced no microevents during descent and landing.
Another provocative finding emerged from analysis of the 40-minute control period for the No-Rest Group crewmembers. On five occasions, crewmembers fell asleep during the 40-minute period when they had been instructed to maintain their regular flight activities. These sleep episodes lasted from a couple of minutes to 14-minutes. These physiologically documented sleep episodes occurred in a NASA/FAA study of fatigue, when volunteers were being physiologically monitored and observed by two NASA researchers on the flight deck. Clearly, this is a situation where crewmembers would have been motivated to maintain their usual flight activities for the 40-minute period. This supports previous information that regardless of training, professionalism, or having the "right stuff," extreme sleepiness can precipitate uncontrolled and spontaneous sleep.
Therefore, the "NASA nap" was associated with improved alertness and performance compared to a No-Rest Group. Based partly on these findings, the FAA requested an industry/government working group to draft an Advisory Circular that would provide guidelines for controlled rest on the flight deck. This proposal is currently under review by the FAA. In the future, controlled rest on the flight deck may be another operational countermeasure available to maintain alertness and performance during long-haul flight operations.
Fatigue Education and Training Module. A goal from the inception of the NASA Ames Fatigue Countermeasures Program has been to return the information acquired to the operational community. To meet this goal, an education and training module entitled, "Alertness Management in Flight Operations," has been developed for the aviation industry (ref. 31). The module is intended as a 1-hour live presentation delivered by a knowledgeable individual. The presentation is complemented by a NASA/FAA Technical Memorandum that contains the visual materials from the presentation and complementary appendices. The appendices provide information on sleep disorders and sleeping pills, relaxation skills, summaries of NASA fatigue studies, and other references for further reading. The module was field tested in twenty-two presentations for over 1,600 individuals at air carriers, military groups, the NTSB, pilot unions, and other forums. The NASA Ames Fatigue Countermeasures Program offers a two-day workshop on implementation of the module and provides training for individuals to become knowledgeable with the material. These individuals then take the information back to their organizations for implementation in appropriate forms and forums. To date, fifty-five individuals representing nineteen organizations have attended workshops, and implementation through annual recurrent training programs and CRM classes is underway at several major U.S. air carriers. For information about the education and training module and participation in the implementation workshop, write to: Fatigue Countermeasures Program, NASA Ames Research Center, MS: 262-4, Moffett Field, CA 94305-1000.
Future Considerations
There are many challenges that lie ahead regarding alertness management in long-haul flight operations. Automation will continue to evolve and be incorporated into long-haul aircraft. In addition to understanding the potential contributions of the automation to boredom and complacency, research and design should examine how the automation could be used to improve alertness and performance. Long-haul aircraft already incorporate onboard crew rest facilities to provide a bunk for sleep when flown with an augmented crew. How these bunks are rostered, the quantity and quality of sleep obtained, the effects on subsequent alertness and performance, and potential improvements should all be considered. Modern aircraft automation is reducing the number of flight crewmembers required for operation. Issues of three- vs. two-person cockpits cross many domains, including the potential effects on fatigue. The global aviation industry is changing and becoming more closely connected and interdependent. Therefore, international regulatory policies regarding flight/duty/rest requirements may have global ramifications. Future development and empirical evaluation of possible countermeasures, such as bright light, melatonin, diet, and exercise require attention as well.
There is sufficient scientific and physiological knowledge to incorporate
our understanding of fatigue factors into approaches that will minimize
the adverse affects and maximize alertness and performance during long-haul
flight operations. This undertaking will require a broad examination of
the aviation industry for specific arenas in which to implement change.
The aviation industry has put tremendous effort into minimizing risk and
maintaining an impressive safety margin demanded by the flying public.
The human factor (i.e., flight and cabin crew, ATC, ground maintenance personnel,
schedulers, and others) will remain a critical component in maintaining
and improving aviation safety. Therefore, the physiological capabilities
and limitations of humans regarding sleep and circadian rhythms will continue
to be important in flight safety, productivity, and performance.