On November 20, 1953, he [Crossfield] became the first man to fly at twice the speed of sound as he piloted the Skyrocket to a speed of 1,291 mph (2,078 km/h, Mach 2.005). The Skyrocket D-558-II surpassed its intended design speed by 25 percent on that day. With 99 flights in the rocket-powered X-1 and D-558-II, he had — by a wide margin — more experience with rocketplanes than any other pilot in the world by the time he left Edwards to join North American Aviation in 1955. As North American's chief engineering test pilot, he played a major role in the design and development of the X-15 and its systems. Once it was ready to fly, it was his job to demonstrate its airworthiness at speeds ranging up to Mach 3 (2,290 mph). Because the X-15 and its systems were unproven, these tests were considered extremely hazardous. Crossfield flew 14 of the 199 total X-15 flight tests with most of these tests establishing and validating initial key parameters. Scott Crossfield not only designed the X-15 from the beginning, but introduced many innovations, to include putting engine controls of the rocket plane into the cockpit. Previously, all engine adjustments resulted from technicians making adjustments on the ground based upon results of flight profiles.
