Question

What happens to the respiratory system of a pilot who is in power drive in a supersonic plane

Answer 1

Due to lack of oxygen, the lungs will start breathing anaerobically i. e, without oxygen . This may lead to cramps.

Answer 2

Almost nothing happens. There is a sudden change in pressure which could cause great amount of damage to the lungs of a normal person bit airplane pilots are trained to withstand such pressure changes.
BUT One thing to be noticed is that there is
!!NO lack of oxygen!!
At high altitude there is less air present but pilots are provided with pressurized oxygen in their masks.

Hope it cleared your doubts.