^^^This. I'm on final approach to Muhammad Ali Louisville International (yes it's really called that, though the code is SDF, for Standiford Field, which is what I call it). SDF is world headquarters for UPS air services, so we have lots and lots of jets overhead. When they ordered the ground stop and all the planes shut down, it was eerily quiet here, too. I'll admit to a little irrational fear when jets did start flying again.
I lived four miles from Dobbins ARB at the time - fighters were scrambling all night on the 11th and into the morning of the 12th.