by Tim Kern
All pilots have experienced it: that heavy, slow-reacting feeling they get when theyre tired. Its a good thing they have done this so many times, that they are so familiar with their cockpits, that the weather was good, that the copilot was such a go-getter…
How dangerous is it to count on all those factors lining up, just to compensate for a lack of rest? Well, as they always say, that depends. Although everyone has a feeling for just how much rest and sleep he needs individually, are there some general guidelines that can be drawn from a top-performing sample of well-trained, well-regulated pilots? Would it be useful to contemplate a study of F-117 Nighthawk fighter pilots, which might help keep some logbooks free from embarrassment or worse? Can those feelings lie?
At the Aerospace Medical Associations 2004 annual convention and symposium in Anchorage, Alaska, a very recent study performed on Nighthawk pilots by a husband and wife team was made public. The findings, though not conclusive, deserve attention in the civilian world.
Drs. Lynn and John Caldwell, both of the Air Force Research Lab, have been studying the effects of fatigue on pilots for over a decade and recently studied volunteer pilots at Holloman AFB, starting at the beginning of a work day and continuing for a total of 37 hours. The study compared the pilots abilities-cognitive, math, simulator flight tasks-over that period to determine what degradation would occur, how much and when. They also monitored pilots EEGs-brain waves-their moods and their psychomotor abilities. Some of what they found questions conventional wisdom on the subject.
As John Caldwell wrote, Long work hours, often without adequate sleep, are common for Air Force pilots who fly long-haul missions. Research shows that performance declines as time awake increases, leading to errors which may create safety hazards. The time at which the most serious degradations occur varies somewhat among individuals and is difficult to predict. If a short test or an unobtrusive physiological measure could accurately indicate whether a pilot is alert enough to complete the mission, safety could be increased by sending out only those pilots whose capabilities have not yet begun to significantly decline.
While the Caldwell study focused on military pilots, there are strong lessons in it for civilians as well.
In The Real World
Although a 37-hour duty cycle wont happen in civilian life, there are plenty of cases where civilian pilots personal schedules may extend beyond all reason. Travel, weather-related delays after the airline work is done, personal obligations-a lot of things can make a pilots rest period merely theoretical. Granted, theres generally nobody shooting at their airplanes, but the fatigue-induced mistakes can still cost plenty.
Pilots moods, vigor and skill all declined rapidly after about 25 hours awake. Though their nutrition was maintained by allowing them to eat regular meals and plenty of snacks, sleep and rest were denied. They noted parenthetically that neither the eating nor the ability to briefly get some morning sunlight helped the pilots overcome the sleep loss.
The Drs. Caldwell found, in general, that the worst period for psycho-motor tracking in the studied pilots seemed to be about one full day into the test period, and the worst period for simulator flight performance occurred a few hours later (often well past sunrise). Towards the end of the sleep deprivation period, pilot coordination and other test parameters actually improved slightly, though never to low-fatigue levels. (The Caldwells make the educated guess that the tiny improvement may have simply been a result of anticipating the end of the study.)
Dr. John Caldwell wrote privately, Also, while performance does tend to either improve or level off at the end of the day, there are a couple of points to bear in mind:
1) This is a temporary circadian effect that pilots often mistakenly interpret as evidence that they are getting used to the sleep loss when in fact they arent (because performance is twice as bad in the subsequent sleep-deprivation period), and
2) By the time they hit the end of the first day, they are already so impaired from the earlier degradations that you wouldnt want to fly with them anyway (even if they never declined by another 1 percent).
Dr. John noted that flight performance tests showed a 30%-80% decrease at the bottom of the curves. There were no crashes, he noted, but there was greatly decreased performance. Test items such as standard turns and approaches, climbs and descents, constantly practiced and routine, also suffered. Even the simple maneuvers dropped badly. He continued, Take my word for it: Ive seen it over and over again in both simulators and actual aircraft.You do not want to be flying with anyone who has been awake for more than 18-24 hours if there is any way you can avoid it!
The study seemed to show that the most dangerous phase of sleep deprivation was in the period 25-30 hours into the test, as each of the parameters peaked (or bottomed out, depending on how you look at it) during that time. The EEG (both Theta and Delta brain activity) showed the brain was particularly tired at roughly the 30-hour mark.
Dr. John Caldwell explained what that means to the layman: It is clear that just one night of sleep loss seriously impairs the ability to perform even routine, well-practiced aviation tasks, while mood and morale decline, and the sleepy brain just refuses to work normally. Whats worse is that when the pilots looked back on their own performance, they often thought they were getting better at the very times at which their skills had deteriorated the most.
What Does All This Mean?
While considerations of individuals personal skill-timing may be predictable and useful at the squadron or fleet levels, just how much that knowledge would help a wing commander (or a dispatcher) remains a mystery. Thinking militarily, would you want a squadron of pilots whose fatigue patterns matched (so you could deploy a squadron at an effective time), or would you like a mixed group, so that, even though one or two of your pilots may be off-cycle, others may not be so badly affected?
Since you cant predict when the enemy may need to be clobbered, you, as a military commander, may choose to have the mixed squad, even though you know that you would be putting an individual pilot or two at greater risk. A large civilian operation may have more options: It can look at schedules and availabilities, and has the option to match a pilot to a trip, to help compensate for individuals fatigue rhythms … theoretically, at least.
Of course, the testing that would be required to set baseline performances for each pilot would be lengthy and expensive; and the Caldwells note that they have not yet determined if any given pilot would have the same response pattern, tested at different times in his life. A test administered on the 25th birthday may not be a good predictor on the 30th, or 50th. Frequent high-stress testing may not be good for pilot health or morale, either.
Where Does It Leave Us?
As with so many interesting studies, the Caldwells have shown that there is something to be gained through this type of research. Just what that is, and how well necessary data can be collected and applied, will be better known in the future. Can the pilots patterns be correlated to something in their DNA? Can specific training and/or nutrition alter a pilots response timetable? It may be possible to find the answers, but then the next question arises: What can we do with the results?
What the Caldwells have led us to is at least some additional understanding. There are four things that are indicated by their results so far:
1) Pilots are different in their responses to fatigue, though some broad patterns do exist.
2) After 18-20 hours without sleep, fatigue will definitely start to rear its ugly head.
3) Even the best-trained, current and qualified, professional pilots are not immune to the serious impact of sleep deprivation.
4) Any boost in performance at sunrise is purely coincidental; it is the duration of the individuals duty cycle, not its timing relative to the sun, that seems to be most important.
Does Get Used To It Work?
Another presenter at the same conference, Dr. David Dinges, Ph.D., noted that sleep deprivation over long periods of time can result in degraded performance, even when the subject doesnt feel sleepy. In a study published in 2003, he and his colleagues wrote that, …it appears that even relatively moderate sleep restriction can seriously impair waking neurobehavioral functions in healthy adults. Sleepiness ratings suggest that subjects were largely unaware of these increasing cognitive deficits, which may explain why the impact of chronic sleep restriction on waking cognitive functions is often assumed to be benign. For the record, Dr. Dinges study covered (non-pilot) subject groups of healthy young adults whose sleep was restricted to four and six hours of sleep per 24-hour period and, in the long term, it found that test results didnt differ significantly between the four-hour group and the six-hour group.
Worse, the results of his tests on the short-sleepers showed results, after two weeks on the low-sleep diet, comparable to those from subjects who hadnt slept at all for two days.
The subjects, though, did not report feeling more sleepy at anything close to the rate of deterioration of their test results, as the days went by. So it seems, no matter how long someone tries to do without regular sleep, the body does not get used to it, though the brain may think it does. The Caldwell study supports this theory: Subjective analysis of how one feels may be the best quick indicator of fatigue as long as the episode of continuous wakefulness is short (i.e., 40 hours). This optimism was tempered by this warning: If using subjective indicators to predict fitness for duty, caution is advised since some people will overestimate their alertness levels and therefore, their cognitive abilities. The bottom line: You may think a week or two of staying up late wont affect your performance. Youre wrong; so, there. Now, go get a good nights sleep.
-Tim Kern is a freelance aviation journalist and feature writer living in Winter Haven, Fla.