Boom, US company’s prototype aircraft XB-1, has broken the sound barrier as the supersonic-test flight breaks the sound barrier. The test opens the way first supersonic passenger jet since Concorde was retired in 2003. During the test the aircraft reached an altitude of 34, 000feet before accelerating to Mach 1.1 speed  (844mph) – 10 per cent faster than the speed of sound (744mph).