SCOTT CROSSFIELD WAS THE FIRST to fly the X-15, and he probably knew the airplane better than anyone else. He had left his job at the National Advisory Committee for Aeronautics in 1955 and gone to North American Aviation, which had just won the X-15 contract, to bring a pilot's perspective to the design. Crossfield was an extraordinary test pilot, but at the end of the first flight, a seemingly simple power-off glide on June 8, 1959, the airplane tested him.
As he approached the dry lake bed at Edwards Air Force Base in California, he pulled the nose up to slow his descent. The nose came up too far, and he had to push it back down—and now he knew, and watchers on the ground knew, that the airplane had entered a divergent oscillation, galloping along a sine wave that increased in amplitude as Crossfield descended. Another X-15 pilot, Milt Thompson, later wrote that it was “a terrifying sight.” Crossfield couldn't stop it, but he managed to get the landing skid on the ground at the bottom of a cycle, saving the airplane and possibly his own life. The problem turned out to be due to a poorly adjusted pitch damper; it was easily corrected.
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