Sonic boom? F15 test flight?


Near 11:30 this morning, I heard a loud thump that I guessed was a sonic boom. I went to and found an F15 that had just briefly gone over 1,100 mph / 957 kts at 40,000 ft.

Taking off and landing from St Louis… McDonnell Douglas the F15 maker and an Air National Guard base are both located there. Test flight of some sort would be my guess. Flight history for this MACRD56 thing shows other occasions of high airspeed and unusually erratic flight paths.

And now I am wondering… would that speed and altitude be likely to cause a sonic boom or not?


That would be correct. At sea level, Mach 1 is 761 mph (662 knots). At 40,000 ft, the speed of sound is 660 mph, (573 knots). So any aircraft flying faster than Mach 1 or the speed of sound would produce a sonic boom.

The jet in question was probably going Mach 1.6 ish, if my math is correct.


I must have been misunderstanding this for a lot of years. I always thought the thinner air at higher altitudes would allow aircraft to go FASTER without exceeding the speed of sound and causing sonic booms.