How can an aircraft travel faster than speed of sound without breaking the sound barrier?
The sound barrier is a function of airspeed and air density. If you have a strong enough tailwind, your ground speed would be above what most lay people would consider the speed of sound without breaking the actual sound barrier.

Aircraft (or any object moving through the air alone) are governed by airspeed. Ground speed is only relevant when traveling on the ground or transitioning to that state (approach to landing).