A strong shock wave generated by an aircraft when it is flying in the earth’s atmosphere at supersonic speeds. This shock wave is radiated from the aircraft, and where it intercepts the surface of the earth a loud booming sound is heard. The loudness depends on the speed and altitude of the aircraft and is lower in level flight than when the aircraft is undertaking a manoeuvre. The maximum increase of pressure in the shock wave during a transoceanic flight of a commercial supersonic transport (SST) is 120 Pa, equivalent to 136 decibels. A great deal of research has gone into the problem of how to make sonic booms less intense, in the hope that this will make supersonic aircraft more commercially viable.