“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.”
On May 20, 1927 Charles Lindbergh began his solo record flight across the Atlantic Ocean; a flight that lasted 33 1/2 hours. No better example of fatigue in aviation can be found than in the historic log entry above, written by Lindbergh during that extraordinary flight.
As we reflect on such aviation feats, one thing is clear; even the best aviators are subject to the insidious and sometimes fatal problem of fatigue.
Fatigue is not a mysterious phenomenon, but rather a well-known and frequently experienced problem that all aviators experience at some point in their flying careers. Unfortunately, the difference between successful fatigue countermeasures and an accident is not always clear. As a result, we need to address the factors that influence the level of fatigue and review some of the possible countermeasures.
First and most important is sleep. Our bodies are designed to work properly only if the natural cycle of sleep is adhered to.
The daily biological clock that regulates sleep is referred to as circadian rhythm and is influenced primarily by light, which in turn influences the production of melatonin. Less light means more melatonin production and more sleepiness.
If sleep does not occur when the body signals it is needed, the circadian rhythm gets out of sync. The ramification of an out-of-sync rhythm is that we are sleepy when awake and wide awake when we’re supposed to be sleeping. Further disruption of the normal cycle can decrease performance, and impact other bodily functions, such as decreasing appetite.
Pilots who fly on the “backside of the clock” (nighttime) are setting themselves up to experience these sorts of problems if their sleep habits are not properly adjusted ahead of time. Recently, we’ve seen lots of press on EMT helicopter accidents, in part attributed to this backside of the clock flying.
Light is not the only factor that affects circadian rhythms however. Other factors include hormones, core body temperature, level of physical activity, average heart rate, and a few others. Considering temperature, very early morning and mid-afternoon appear to be the two times of the day where body temperature is the lowest, corresponding to when we feel maximum sleepiness during the day. If you are flying during these periods, stay vigilant and try to stay actively engaged in flying the airplane.
Heart rate and physical activity are closely related, so any activity that increases physical activity will also help keep the pilot awake. The flip-side is that physical activity such as exercise at the wrong time of the day (e.g. when the body is supposed to be asleep) can screw up the biological clock. One source recommends at least four hours between exercise and sleep so as not to over-stimulate the body, thus leading to more difficulty falling asleep.
In general, the longer we try to stay awake, beyond about 16 hours a day, the harder it becomes. If an attempt is made to stay awake significantly longer than normal, the body may actually continue to function adequately, but cognitively speaking, judgment and decision-making skills will start to decline rapidly.
Research has shown that the average person needs around 8 hours of sleep a night. However, the individual range is anywhere from around 4 hours, to better than 10 hours. As a result, the “average” person does not necessarily mean the “normal” person.
The only way to determine your own sleep needs is to shut off the alarm clock for several days and see how many hours (on average) it takes for you to wake up feeling rested. If you never feel rested, then something is wrong and you need to see a doctor about it.
When trying the sleep experiment to determine your own sleep needs, bear in mind that most of use are sleep deprived to some extent, so it can take time for the body to recover. Sleep deprivation is cumulative, but sleeping extra tomorrow will not resolve the hours you lost last night!
You have to sleep the right number of hours (whatever is right for you) consistently for a period of time before sleep deprivation is resolved. In other words, sleeping late on the weekends is not an effective way to make up for short nights during the week. Likewise, the body does not store up “sleep credit” that can be traded for short nights down the road.
In fact, over sleeping can make you even groggier during the day. This is partly because the body gets confused on whether its supposed to be sleeping, or awake if sleep is attempted longer than is really needed.
One countermeasure to fatigue is knowing when rest or sleep is needed, but can you accurately tell how tired you are? Research shows people are terrible at making an accurate assessment of their own tiredness, and one study from NASA showed that participants reported maximum alertness at times when the subsequently fell asleep the fastest. Oops! That’s bad news.
However, the good news is that we are quite good at seeing tiredness in others. So a really good countermeasure is to take somebody with you when you go flying on long trips or on the backside of the clock. The risk of not doing so is that once the body reaches a certain point, it will go to sleep whether you want it to or not. You are hopefully in bed when that happens but sometimes it happens in the cockpit.
There have been several instances of what the professionals call “mirco-sleep” in the cockpit where both pilot and copilot where literally counting sheep during critical phases of flight. It can happen so fast and last for such a short time that you don’t realize you’ve gone to sleep. Boredom doesn’t cause that; fatigue from sleep deprivation does!
Another countermeasure to fatigue is to recognize the warning signs (and then of course do something about it). Among the warnings signs that top the list are: vision going in and out of focus, head nods (bobs), excessive yawning, poor motivation, forgetting recent activities, missing checklist steps, impatience, poor attention to detail or accuracy.
Doing something about these warnings signs includes: talking with the other pilot or passengers, doing something physical in cockpit with the arms and legs, turn up the lights if its dark, drinking fluids and maybe caffeinated drinks. Staying engaged in flying is the key to staying awake.
Preventing fatigue can be difficult once in the cockpit, especially on long flight, but luckily there are some countermeasures that can be employed on the ground prior to flight. Diet is one way to help. There are any number of sleep inducing foods that need to be consumed with discretion. Likewise, there are foods that act as stimulants and may actually help counter short-term fatigue symptoms.
The list of sleep inducing foods is long so I encourage each of you to go online and self-educate. In general, it is best not to consume large meals within about two hours prior to the temperature low points talked about earlier.
Stimulating foods will help stave of the desire to nod off. Caffeine has historically been the stimulant of choice, but it is used incorrectly more times than not. First, caffeine needs about 15-30 minutes to reach its maximum effectiveness after ingestion so it needs to be ingested at the right time during the flight. The exact amount needed is determined by individual’s differences but what is known is that smaller, regular doses during a period of activity are usually more effective than a single large dose at the beginning.
Another danger of a large single dose of caffeine prior to flight is that the withdrawal symptoms after the caffeine wears off present a performance risk, especially during later high-stress phases of flight like landing. Also realize that caffeine should be limited to only when it is absolutely needed, otherwise addiction is a real possibility.
The problem with addiction is that the body needs it to feel “normal” but you will not be mentally “normal” while addicted to caffeine. By all means, please realize that caffeine may be a temporary fix for fatigue, but it is certainly not a long-term solution. It’s not fixing the underlying problem that causes fatigue in the first place.
Also, from what I’ve read on the topic, a well-balanced diet without caffeine of any kind, and proper sleep is the best solution to avoiding fatigue during the waking hours. That’s just not possible for everyone, or all the time, so simply be aware of when your diet and/or sleep is lacking and realize that fatigue is more likely under those circumstances.
The bottom line when considering the fatigue problem is that sleep is a physiological necessity. If you need to fly at a time when you normally sleep, try to adjust your sleeping schedule ahead of time so your circadian rhythm has time to adjust. Use countermeasures that I’ve mentioned to stave off fatigue in the cockpit and take someone along with you if at all possible.
And finally, realize that what you do during your time off from flying affects your performance in the cockpit. Sleep well, eat well, and get exercise. Sounds like good advice whether you fly or not!
This month’s Pilot Primer is written by Donald Anders Talleur, an Assistant Chief Flight Instructor at the University of Illinois, Institute of Aviation. He holds a joint appointment with the Professional Pilot Division and Human Factors Division. He has been flying since 1984 and in addition to flight instructing since 1990, has worked on numerous research contracts for the FAA, Air Force, Navy, NASA, and Army. He has authored or co-authored over 180 aviation related papers and articles and has an M.S. degree in Engineering Psychology, specializing in Aviation Human Factors.