Airspeed Record of Mach 6.72 (4,543 mph, 7,297 km/h) in a North American X-15

On October 3, 1967, a North American X-15 was dropped at 45,000 feet (13,716 meters) over Mud Lake, Nevada.

Pilot William J. “Pete” Knight fired the rocket engine and began to climb and accelerate. The X-15A-2 climbed to 102,100 feet (31,120 meters) and Knight leveled off, still accelerating. After 140.7 seconds of engine burn, Knight shut the engine down. The thrust seemed to decrease gradually and the X-15 continued to accelerate to 6,630 feet per second (2,021 meters per second), or Mach 6.72. Knight entered the high key over Rogers Dry Lake at 55,000 feet (16,764 meters) and Mach 2.2, higher and faster than normal.

Knight touched down after an 8 minute, 17.0 second flight. His 4,520 mile per hour (7,274 kilometers per hour) maximum speed is a record that still stands as the fastest flight of a North American X-15.