12 December 1953 – 
Mach 2.5 (2 ½ times the speed of sound) is achieved for the first time by Major Charles “Chuck” Yeager in the Bell X-1 A. The rocket-propelled experimental aircraft reaches 1,650 mph (2,660 km/h) at 70,000 ft (21,000 m).
This photo of the X-1A included graphs of the flight data from Maj. Charles E. Yeager’s Mach 2.44 flight on December 12, 1953. (This was only a few days short of the 50th anniversary of the Wright brothers’ first powered flight.) After reaching Mach 2.44, then the highest speed ever reached by a piloted aircraft, the X-1A tumbled completely out of control. The motions were so violent that Yeager cracked the plastic canopy with his helmet. He finally recovered from an inverted spin and landed on Rogers Dry Lakebed.
Among the data shown were Mach number and altitude (the two top graphs). The speed and altitude changes due to the tumble were visible as jagged lines. The third graph from the bottom showed the G-forces on the airplane. During the tumble, these twice reached 8 Gs or 8 times the normal pull of gravity at sea level. (At these G forces, a 200-pound human would, in effect, weigh 1,600 pounds if a scale were placed under him in the direction of the force vector.) Producing these graphs was a slow, difficult process. The raw data from onboard instrumentation recorded on oscillograph film. Human computers then reduced the data and recorded it on data sheets, correcting for such factors as temperature and instrument errors. They used adding machines or slide rules for their calculations, pocket calculators being 20 years in the future. (1)
Hear his cockpit voice recorder at https://soundcloud.com/sgt_carbonero/x-audio-crop-mod
Source: Chuck Yeager.org Mach 2.44 Flight in the X-1A; Wikipedia