Scott Crossfield, a legendary test pilot, died Thursday in an apparent plane crash. He was 84.

Crossfield was the first pilot to fly the X-15 and the first pilot to fly at Mach 2 and (unofficially) the first to fly at Mach 3 successfully

World War II fighter pilots discovered control problems in high-speed dives due to what was later found to be supersonic shockwaves building over their aircraft, the so-called sound barrier.

The late 1940s through the 1960s became a golden era of flight test, all centered at what is now Edwards AFB in Southern California's high desert.

1942: Development of America's first jet, the Bell P-59, was tested at Muroc Army Airfield.

1947: Air Force test pilot Chuck Yeager flew the rocket-powered X-1 in the world's first supersonic flight.

The X-15 rocket plane helped open the door to manned space flight in the late 1950s and 1960s

Sources: NASA , AV Web.