The correct answer is: Subsonic.
Subsonic speed is the speed of an object that is slower than the speed of sound in the surrounding medium. The speed of sound in air at 30°C is 343 meters per second, or 1225 kilometers per hour. Therefore, an aircraft flying at a speed of 1260 kilometers per hour is flying at subsonic speed.
Sonic speed is the speed of sound in a particular medium. The speed of sound in air at 30°C is 343 meters per second, or 1225 kilometers per hour.
Supersonic speed is the speed of an object that is faster than the speed of sound in the surrounding medium. An aircraft flying at a speed of 1260 kilometers per hour is not flying at supersonic speed.
Mach is a unit of measurement for speed equal to the speed of sound in a particular medium. The speed of sound in air at 30°C is 343 meters per second, or 1225 kilometers per hour. Therefore, an aircraft flying at a speed of 1260 kilometers per hour is flying at Mach 0.93.