Q. about "Flight Level"

"TeleTech" wrote in message
. 193.32...
Hi.

I have heard some military comms on my scanner (not that I understand
everything I hear).

If I understand correctly, "Flight Level" or FL is used to describe
altitude. So, FL400 would be 40,000 feet?

My question is, if an airplane is way up there, can I hear the plane down
here? (I can hear them on the radio, but I mean, can I actually hear the
engine of the jet, as in the sound that a jetliner makes when it goes
overhead.)

At the speeds used up that high, wouldn't I hear a sonic boom?

You'll hear them at 40,000ft. That's only 7 miles away and there's nothing
to get in the way.

If they were travelling at mach speeds you'd hear the boom but they don't
tend to do that over land, or at least over populated areas.