As an airplane approaches the speed of sound, shock waves build up,
creating increase in drag, loss of lift, and loss of control. Fifty years ago,
it was thought that a plane would break up under these conditions. When
traveling near the speed of sound, the plane came up against a "sound
barrier"—as though the velocity of sound represented a wall through which a
plane could not move. With technological advances such as more powerful engines
and improved airframe and wing design, the sound barrier was broken in 1947.
Once an airplane crosses the sound barrier, the flight is smooth.