Just like to point out that a person on the ground cannot hear
the boom unless the aircraft is flying faster then the speed of
sound at ground level. So... assuming the air is dry and 20C
that mean if an aircraft is flying Mach 1 at 30,000ft a person
on the ground wont hear the shockwave (boom) unless the aircraft
is flying faster then 343.2 metres per second (768mph) at ground
level. If the speed is slower the shockwave will actually curve
back upwards. You can hear the boom at any altitude, for example
shooting out in the desert of Barstow CA. In the middle of the
day you couldn't see the fighters most of the time BUT you could
definitely hear the boom from the ground. Sounded like a bomb
detonation in the distance at first. Sorry Blaze, but the
shockwave will not reach the ground unless the aircraft is going
faster then the speed of sound at ground level. When you hear
the boom out in Barstow it's because those aircraft are flying
faster then the speed of sound at ground level. From the US
Airforce... Soni