December 1, 2005
What did the Chernobyl and Three Mile Island nuclear accidents, the space shuttle Challenger explosion, and the Exxon Valdez grounding have in common? Answer: The official investigations in each case determined that fatigue played a causal or contributory role in the outcome.
According to Mark Rosekind, a leading expert on fatigue and alertness, accidents like these are especially dramatic examples of what can happen when humans become fatigued. But each year thousands of other less spectacular accidents occur across a range of activities, a by-product of a 24/7 world where sleep loss and circadian disruption are the norm for many individuals. For example, by one estimate as many as 100,000 auto accidents in the United States each year result from driver fatigue, causing an estimated 1,500 fatalities and 76,000 injuries.
Aviation has had its share of fatigue-induced accidents too. That's why Rosekind was invited to be a featured speaker at Bombardier Aerospace's 2004 Safety Standdown in Wichita, an annual corporate aviation safety conference the aircraft manufacturer hosts. Rosekind is president and chief scientist of Alertness Solutions, a firm that specializes in developing practical strategies to combat the effects of fatigue. A former researcher for NASA, he has clients including airlines, railroads, corporate flight departments, and other organizations looking to reduce or eliminate fatigue-related incidents, accidents, and lost productivity. And while fatigue is an admittedly tiring subject, fortunately for those in the audience, Rosekind's speaking style was anything but. He put on a lively, fast-paced presentation that was both entertaining and informative — I wasn't once tempted to doze off.
Fatigue has been a factor in aviation accidents large and small, including the 1993 crash of a McDonnell Douglas DC-8 cargo plane during a landing attempt at Guantanamo Bay, Cuba. In that accident the NTSB ruled that "the probable causes of this accident were the impaired judgment, decision-making, and flying abilities of the captain and flight crew due to the effects of fatigue." This marked the first time in the NTSB's history that the agency identified fatigue as a probable cause of a major U.S. aviation accident. (Rosekind was a NASA researcher at the time and one of the scientists who examined fatigue factors in this accident at the request of the NTSB.) Four years later the NTSB ruled that fatigue was a contributing factor in the 1997 Korean Air Boeing 747 controlled flight into terrain (CFIT) accident in Guam too.
It can be difficult to conclusively prove that fatigue caused a particular accident. That's one reason the NTSB took as long as it did to finally recognize its role in a major accident. But Rosekind points to a growing consensus among scientists that official accident statistics greatly understate the problem. Across all modes of transportation, as many as 15 to 20 percent of accidents are likely fatigue related. Put another way, fatigue is probably a factor in more accidents than drugs and alcohol combined. Therefore, it's likely that fatigue has played a role in a large number of aviation accidents where it was not specifically identified as a factor.
We all know what it's like to feel tired, but from a scientific viewpoint, fatigue is primarily the result of two physiological factors — sleep and the circadian clock.
Sleep, according to Rosekind, is as critical to human survival as air, food, and water. Adults tend to require anywhere from six to 10 hours nightly, with around eight hours being the average. The amount an individual needs is probably genetically determined and can't be changed. When we don't get enough, the "lost" sleep accumulates into a sleep deficit. As the deficit grows over multiple sleep and wake cycles, fatigue increases, our performance and alertness levels deteriorate, and our health can suffer.
Many factors affect the quality and quantity of sleep we get each night, but age, alcohol use, and sleep disorders are probably the biggest variables. According to Rosekind, more than 90 sleep disorders have been identified, many of which make it difficult for the sufferer to get the needed amount of sleep. As we age, we actually become more susceptible to developing sleep disorders, and there's a greater chance their effects will be more severe. Even if you don't develop a sleep disorder, after age 50 the amount of deep sleep you manage to get each night will probably start to decrease. Many people turn to alcohol, the most widely used sleeping aid, to try to make up for these disruptions. But alcohol actually has the opposite effect, as it tends to reduce both the length and the quality of sleep.
The other big determinant of your alertness and performance levels is the circadian clock, a brain function that controls the approximately 24-hour cycle of sleep and wakefulness. The circadian clock is most affected by light. Gradually changing the cycles of light and dark can reset your circadian clock to a new time zone or schedule shift. But doing so abruptly — flying across many time zones, for instance — causes your circadian clock to become desynchronized. This negatively affects almost every aspect of your performance, including overall mood, decision-making skill, reaction time, memory, ability to communicate, and alertness.
There are two distinct periods of alertness and two periods of tiredness in each 24-hour cycle. For most people, maximum tiredness occurs at the low point in the circadian cycle from about 3 to 5 a.m., with a second period of tiredness 12 hours later from 3 to 5 p.m. The two windows of maximum circadian alertness occur from approximately 9 to 11 a.m. and again from 9 to 11 p.m.
Interestingly enough, the Guantanamo Bay accident occurred during the afternoon low point in the circadian cycle. Two of the three crewmembers had an acute sleep loss in the 72 hours prior to the accident, and all three had a significant accumulated sleep debt over that time. Each also had been continuously awake a long time, ranging from 19.5 to 23.5 hours.
Rosekind has studied the effects of fatigue in all kinds of flight operations, including long- and short-haul airline operations, overnight cargo, corporate, and charter flying. While they differ in style, each can be fatigue inducing in its own way. (Even if you don't fly a full-time flight schedule for a living, you can still find yourself piloting an airplane while tired on any given day.) One thing holds true across the board: When a pilot gets fatigued, performance suffers and an accident becomes more likely. In one study of corporate flight operations conducted by Rosekind's firm, pilots identified long duty days, early morning departures, multiple legs, night flights, and weather issues as being the top five factors that led to fatigue. And 85 percent of the corporate pilots surveyed felt that fatigue represented a moderate to serious safety issue.
So what does all this mean to pilots? In short, fatigue might be an inevitable part of flying, but there are things you can do to minimize its dangers.
Rosekind suggests the first thing is to educate yourself about the subject of fatigue so you can recognize when you're most at risk. The next step is to put in place some practical alertness strategies to keep from becoming a statistic. Rosekind says there is no one-size-fits-all solution, but there are many coping mechanisms that can help, depending on the individual. Here are just a few of his recommendations:
In an anonymous survey of 1,488 corporate pilots conducted by Rose-kind's firm, the most common techniques used to deal with fatigue during a flight (in descending order of popularity) were moving or stretching, trying to keep busy in some way, hydrating, engaging in conversation, and drinking caffeinated beverages. Falling back on standard operating procedures and good crew resource management skills came next, followed by eating and napping (presumably with another pilot awake to watch the store), and finally raw concentration.
No pilot wants to fly when fatigued. But the reality is, like it or not, you'll probably find yourself flying sometime when you'd rather be snoozing in an easy chair. Recognizing the danger and knowing which countermeasures work best for you can help ensure you reach that easy chair after all.
Vincent Czaplyski holds airline transport pilot and flight instructor certificates and is a Boeing 737 captain for a major U.S. airline.
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