Too Tired to Fly?

May 1, 2001

Lessons in sleep deprivation from Lindbergh and the crew of Voyager

Sleep deprivation, often trivialized or ignored by pilots, nearly brought down two of the most famous aircraft in the world: the Spirit of St. Louis (1927) and Voyager (1986). The thoroughness of the flight planning seemed almost obsessive; to reduce weight and extend range, Lindbergh trimmed the edges from his charts, and one of the Voyager pilots, Jeana Yeager, clipped off her long tresses. But although these pilots had previously experienced the devastating effects of sleeplessness, they put the originally proposed countermeasures on the back burner - and they paid dearly for it.

The effects of sleep deprivation on Lindbergh and the Voyager crew were dramatic - so much so that they may not seem relevant to contemporary commercial or general aviation. Nevertheless, understanding these difficulties and the reasons that they happened will help today's pilots to develop countermeasures.

New York to Paris

Try to imagine embarking on one of the most difficult flights ever attempted after not sleeping for 23 hours and then enduring another day and a half of sleep deprivation. It was "the most difficult and dangerous factor" of Lindbergh's New York-to-Paris odyssey, he wrote in his book Autobiography of Values. During the flight, Lindbergh hallucinated. He thought he was visited by ghostlike apparitions that appeared in his cockpit and even gave him directions. And yet, he was nearly as alert when he landed after not sleeping 56 hours as he was at takeoff, although he almost lost it in between.

Lindbergh was no stranger to physical or psychological challenges, and he knew what he might encounter on the flight. As a mail pilot, he had often flown at night with little or no sleep for a previous day or two. But en route to Paris he flew an unstable aircraft, navigated by dead reckoning, and flew some 15 hours on instruments through a well-developed weather front with nothing but needle, ball, and airspeed. He contended with icing conditions and cockpit temperatures as low as minus 23 degrees Fahrenheit; with his six-foot, four-inch frame sandwiched into the Spirit of St. Louis' tiny cockpit, his face was barely two feet from the instrument panel that blocked his forward vision. Yet none of these or many other challenges - taken alone or together - compared with his sleeplessness, which prompted him to observe, "There comes a point when the body's demand for sleep is harder to endure than any other pain I have encountered."

Only recently have scientists focused on the implications of sleep deprivation for contemporary civilian and military aviation, even space flight. Professor David Dinges at the University of Pennsylvania Medical Center, who runs one of only two sleep deprivation labs in the world, is a leader in the field. "I became interested in the Lindbergh experience because, for the past 20 years, my laboratory has done research for various federal agencies - the National Institutes of Health [NIH], NASA, and DOD, as well as the Naval Research Labs and the Air Force Office for Scientific Research," says Dinges. "We have a longstanding interest in sustained operations and, in particular, how people stay awake and alert in airplanes over a long period of time."

One of Dinges' graduate students counted the number of words in Lindbergh's account of his flight in his book The Spirit of St. Louis, which dealt with Lindbergh's perceived need to sleep. The student tallied the references to sleep and a numerical scale was constructed to quantify the severity of his exhaustion. So many words scored 4, fewer was 3, fewer still was 2, and no mention at all was 1. These were plotted across the flight and compared with 16 test subjects who were kept awake 88 hours. The curve perfectly matches Lindbergh's circadian profile - a rhythmic cycle recurring at approximate 24-hour intervals - and closely correlates with those of the test subjects. As the chart (p. 110) illustrates, Lindbergh became sleepier and sleepier until he started a new biological day.

"Lindbergh is a natural experiment," says Dinges. "But my primary interest was not so much in the flight per se, but rather the detailed analysis of his sleep prior to the flight, and his behavior and performance during the flight - his own sense of what was happening to him. So the primary focus of our investigation was what did he actually do during the flight, how sleepy did he become, and how did he resist the sleepiness." Out of desperation to stay awake, for example, Lindbergh flew low over the ocean so that he could get sea spray in his face through the side windows. He wouldn't eat food for fear that it would further contribute to his falling asleep. "There are segments of his logbook with no entries which means he very likely was in full-blown reverie - stage one reverie, which is a period right between awake and asleep," says Dinges.

One of the main reasons for Lindbergh's fatigue was the "sleep debt" with which he started his flight. This is the difference between the amount of sleep a person needs and the amount he or she gets. As Dr. Melissa Mallis, principal investigator for the Fatigue Countermeasures Program at the NASA Ames Research Center, puts it, "Sleep loss can be additive and can result in a sleep debt. A sleep debt can occur during erratic flight operations when the person's biological timing for sleep does not coincide with the actual time allowed for sleep."

Around the world in Voyager

"Edwards Tower, this is Voyager One. We're ready to go."

"Roger, Voyager One. You're cleared for takeoff. ATC clears Voyager One from Edwards Air Force Base to Edwards Air Force Base via flight plan route. Maintain 8,000. Godspeed."

And so, with 26,366 miles to go, Voyager began its epochal nonstop flight around the world. With pilot Dick Rutan at the controls and copilot Jeana Yeager reading off airspeeds, Voyager started down Edwards' main runway - at 15,000 feet, the longest in the world. The takeoff roll was 14,200 feet.

To understand fatigue problems on the flight, one has to know a bit about the flight crew, the ground crew, and this most unusual single-mission aircraft. There never has been and never will be another like it.

Dick Rutan is a former Air Force navigator and fighter pilot. He volunteered for three tours in Vietnam where he flew 325 combat missions in F–100s. He escaped from North Vietnam after being shot down on his last mission. After completing his Air Force career, he joined his brother, Burt, as the chief experimental test pilot for the Rutan Aircraft Factory - where he set many world speed and distance records in Vari-EZ and Long-EZ aircraft.

Jeana Yeager is a world-class pilot with numerous world speed and distance records. Perhaps most important, she provided much of the motivation and leadership that kept the Voyager volunteers together during the agonizing five years from the conception of the idea to liftoff. This was especially important because the entire program was conducted without government funding.

The flight was Burt Rutan's idea. The world-renowned aircraft designer designed the airplane from composite material half as heavy as steel but five times as strong. It has a canard and twin booms replete with 16 fuel tanks that feed into a single main tank. The system held 7,011 pounds of fuel that powered two Teledyne Continental engines in tandem: a four-cylinder, aircooled, 130-hp O-240 in front, and a four-cylinder, liquid-cooled, 100-hp IOL-200 in the rear.

Voyager's "cabin" and cockpit were telephone booth-size - about three and one-half by eight feet - and the flight characteristics were, well, peculiar. The wings flapped up and down a disconcerting 30 feet; the pilots knew their airplane would disintegrate if they hit even moderate turbulence; and, worst of all, above 83 kt, the flapping wings sometimes oscillated, doubling in amplitude with each cycle. Whether or not the autopilot was engaged, the extremely tricky recovery maneuver from this "pitch porpoise" had to be made within 20 seconds. Yeager never had the time to learn to recover, and Dick Rutan never had the patience or, he says, "the guts" to teach her.

While flying a Long-EZ during a closed-circuit record distance flight between Bishop, California, and Mojave in 1979, Rutan encountered gremlins just as Lindbergh had. He had a huge sleep debt going into the flight and was shaken by the experience. "I had no idea what was happening...little green people told me I had already died. They described what happened - you know, the fiery wreck. ‘You are actually dead, so come with us. Just come with us and we'll handle it. We know you're tired.' I had gone into a different realm I was not even aware of - needing sleep so desperately and trying to go to sleep a little bit and then going fully to sleep when you can't do anything about it." As a result of this experience, Rutan and Yeager visited scientists at the NASA Ames Research Center before their flight in Voyager. They learned that Rutan's hallucinogenic experiences were not pathological, but rather a predictable result of sleep deprivation, and they learned about the insidious subtleties of sleeplessness and fatigue. Most important, they learned about countermeasures - things that pilots can do to prevent or mitigate the effects of sleeplessness.

Following the visit to NASA Ames, Rutan secured another distance record flying from Anchorage to the British West Indies. The flight lasted almost 30 hours, and his new insight served him well: "I got myself set with my circadian rhythms. Most people would go out to dinner and a show, but I would go to sleep at six o'clock so I would be fully rested and adjust my circadian rhythms so when 0300 [3 a.m.] rolled around, that had become my regular getup time. I spent 10 days up there getting on that circadian rhythm. I also exercised and ate right. And to combat sensory deprivation - to make sure I just didn't sit there [during the flight] with nothing to do - I took along Saturday night radio mystery hour tapes - little melodramas like 'The Shadow Knows.' So every time I wasn't talking to air traffic control or just sitting there droning away, I'd pop one of those tapes in and, before I knew it, 20 minutes had gone by."

Rutan and Yeager flew Voyager on a record-breaking four-and-one-half-day closed-circuit course to "warm up." But, as Yeager says, "We weren't able to adjust our circadian rhythms as we should have - there was just too much to be done." Rutan stayed in the pilot's seat for three full days, making do with 10-minute catnaps. Then, to the delight of the ground crew, he finally relinquished the pilot's seat to Yeager and slept five hours. It was the first time he had truly slept aboard Voyager.

On the round-the-world flight, Rutan once again stayed glued to the pilot's seat for three days until the pitch-porpoise problem was behind them. He says his 10-minute naps were effective, but that "it was difficult to be drawn out of that sleep to be functional, and it would take maybe 30 or 40 seconds."

Throughout the nine-day flight, constant weather problems and emergencies meant Rutan averaged only two to three hours' sleep, and he eventually "hit the wall." He thought he saw the instruments bulging out at him, and it took Yeager a solid hour to quiet him down and get him to sleep. Then, when weather forced the flight to 20,000 feet, Yeager's head cold, extreme fatigue, and hypoxia caused her to pass out, and she momentarily stopped breathing. "Except when I was oxygen deprived, I never did sleep solidly; I just took cat- naps," she said. "Instead of nine days, it seemed like just one long day; I didn't really look at a clock to get the time - it was more a data point."

The closest call of the flight came when the oil pressure dropped suddenly and air was introduced to the rear engine. There was some question as to whether Yeager had neglected to monitor the system or if Rutan had turned the oil replenishment crank in the wrong direction. Either way, it was undoubtedly because of the pilots' extreme fatigue.

After nine days, 3 minutes, and 44 seconds, Voyager landed at Edwards, having achieved what many agree was the last significant milestone in atmospheric flight. As Technical Director Jack Norris said, "I've always seen Voyager as a mini homegrown moon program."

Lindbergh and the Voyager crew anticipated constant, unrelenting sleeplessness and fatigue, but general aviation pilots usually don't face such severe problems. Still, we live in a culture that attaches less and less importance on sleep because of our frenetic lifestyles. As Rutan says, "There is a big, often fatigue-related problem among GA pilots, myself included. We often feel compelled to get where we need to go or we get a case of ‘get-home-itis.' Either of these things can result in bad decisions, especially when fatigue is in play.

"All too often there are critical meetings to attend at our destination or back home that can lead us to press minimums when we shouldn't - the kind of decision you are more apt to make when you're tired. But I've learned. I recently had a court appearance in a distant city that could have altered my entire future. The weather at my destination was down to minimums and forecast to deteriorate further as a weather system moved in. So I left a day early, stopped 150 miles short of my destination, and drove the rest of the way in a rented car. If I hadn't done this I would have been fighting ice, trying to get into some at-minimums airport."


Bruce Frazer, AOPA 3502125 , of Arlington, Virginia, is a former Army aviator and demonstration pilot for Bell Helicopter.