United States Air Force Lieutenant Colonel Kevin Henry thought the tiny red dots on his skin were insect bites. But as he relaxed at a Florida beach house with a fellow pilot on a day off in 1990, he noticed he was the only one getting bitten. Henry wouldn’t learn until later that the dots were capillaries breaking under the strain of nitrogen bubbles that had formed during his latest flight in a Lockheed U-2 spyplane, 10 hours earlier. He would find out the hard way how much worse it could get.
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Henry had been flying the U-2 since 1987, and has seen it go from flying over South Korea and Panama to being a constant presence over battlefields in Afghanistan and, until last year, Iraq. Like most others in the elite club of U-2 pilots (there are only 35 to 50 actively flying at any time), Henry is tough and matter-of-fact, but also somewhat romantic about flying the famous jet at 70,000 feet, twice the cruising altitude of commercial airliners—high enough to see the curvature of Earth.
But flying so high has a cost. The dots that Henry saw on his skin and the itching, crawling sensation that he felt were just a couple of the symptoms of altitude-induced decompression sickness. Most people know DCS by its common name, the bends, a condition suffered by divers who rise too quickly from the high pressure at depth to the lower pressure near the water’s surface. (In medical terms, “bends” refers only to the DCS sufferer’s joint pain.)
Pilots can experience the same physical reactions by flying up into the thin air at high altitudes. U-2 pilots are especially at risk, not just because of their extreme altitude but also because their cockpits are only partially pressurized. The pressure in a U-2 cockpit at typical mission altitude is equivalent to the atmosphere at 29,000 feet—as high as the summit of Mt. Everest. To cope, U-2 pilots breathe pure oxygen for an hour before their flight and wear a kind of pressurized spacesuit. Pre-breathing oxygen helps purge nitrogen from their bodies. If nitrogen remains even after pre-breathing and the pilot goes up, the thin atmosphere will cause the nitrogen dissolved in the body’s blood and tissue to essentially boil. The same principle is at work when you open a can of soda: Release the pressure and the dissolved gas rushes to escape, in the form of bubbles. In the human body, bubbles can cause extreme pain, bruising, brain damage, and, without treatment, death.
In March 2006, Henry started experiencing symptoms more severe than the itchy dots he’d had 16 years earlier. This time, however, he was several hours into a combat mission, in support of Operation Enduring Freedom in the Middle East, and more than 13 miles above the ground. “The first thing that happened was the pain in my knees,” he says. “I kind of blew it off because it was very, very light. But this was bilateral”—the pain was in both knees. “They never taught us before: Bilateral is bad. So I just pressed on, of course; that’s what we do.”
Over the next five hours, Henry developed an intense headache, nausea, and extreme fatigue. The pain got worse. At one point, he hallucinated that the airplane had rolled 30 degrees to the left. He began to feel disoriented and sluggish, a sensation he likens to intoxication. At one point, he snapped awake, not realizing he’d dozed off.
“That’s when I go, Okay, I’m not feeling well, and I had to fess up,” he says. He hadn’t wanted to be grounded due to what he thought was an inconsequential medical problem, or to let the younger pilots hear that he returned complaining of a mere headache.
Henry contacted his ground mission supervisor, who woke up the squadron commander back at Beale Air Force Base in California. By that point, Henry had essentially forgotten how to fly his airplane.
Like Henry’s red dots, many symptoms of DCS don’t show up until after a pilot has landed, sometimes days later. The symptoms can be as minor as a headache or fatigue, so they’re often ignored or attributed to dehydration, lack of sleep, even caffeine withdrawal. Says Henry: “We didn’t talk about it, because back when I was growing up in the program it was like ‘Oh, you’ll get grounded.’ ”
Even though pilots were cautious never to appear too sick to fly, true DCS cases also used to be somewhat rare, and severe cases almost unheard of. Pre-breathing oxygen and a strict regimen of rest between flights were enough to keep pilots healthy. For decades, it was enemy fire, not nitrogen bubbles, that worried them.