Doug:
The profile called for climbing to FL400, and accelerating in burner until the intakes started to "program." Mach-2 class fighters have variable geometry intakes, which start to close-off at high speeds (the air that gets inside the intake then expands, slows down, and is therefore subsonic by the time it gets to the engine). Compressors don't like supersonic air--they tend to compressor-stall.
Incidentally, this was a slow process: it took about 120 miles, and you would gain about 3 knots a second. The air is pretty thin at FL400, so thrust---even in burner---is low.
The big "splitter-plate" (vertical board of the intake, next to the fuselage) would start to creep out at about 500 kts indicated. The Mach was usually between 1.7 and 1.8; depending on OAT.
Still in burner, you would climb to FL480, and then take them out of burner (one at a time) to make sure:
1. The engine(s) didn't compressor-stall, cough, and flameout (going in or out of burner sets up huge pressure-transients in the engine...perfect set-up for a compressor-stall)
2. Moments later, when re-initiating burner, that it wouldn't cough as above.
During the "zoom" to FL480, it was easy to overshoot and end up higher (FL520 was my highest; a guy in my squadron had been to FL630, and one backseater had been to FL820).
After the re-light, we needed to get down to about 15000 for some other checks, so you went to idle (again, one at a time!), and glided down. That was where I saw the 230 kts / just above the Mach. During this glide, the landing-gear warning system would be flashing, because it thought "He's below 240 knots, and the gear isn't down!"
Never mind that we were still 8 miles above the ground and still supersonic.
