Why do airplanes are not allowed to travel at the same speed as sound?

Question

Airplanes only travel below the speed of sound, or faster. Why?

Answer 1

because, the airplane will over heat due to the over speeding and the airplane may be burned.  

Answer 2

Interesting question.

If an airplane flew at the speed of sound, the sound -  the wavefront of the sound -  that the airplane itself HAD made would always be in the same place as the plane: they would both move forwards together. So the sound the plane made would be constantly adding to the sound the plane had made - the 'old' sound that was travelling along with the speed-of-sound plane.

The leading sound wave would get louder and louder and LOUDER, as the new sound from the plane kept adding to the "old" sound.

These sound waves would quickly become very powerful, powerful enough to be called "shock waves", They would not only be very VERY loud, but which would actually destroy the plane with the force of their vibrations!

If the plane is traveling faster than sound, this does not happen, because the new sound has left the old sound behind, and it does not happen if the speed of the plane is less than the speed of sound, because the old sound will have left the plane behind.