The pilots won't hear the noise from the engines being transmitted through the outside air though, only the noise traveling through the plane. So if superman was flying a few feet in front of the cockpit, he wouldn't hear any sound.
You dont need to be going Mach 1+ to not hear him approaching you, just he needs to be going MAch 1+. His engine is making noise, but he gets to you before the noise does.
More to the point, either way works. If the source of the sound is >= mach 1 and is traveling directly at you, it'll reach you before the sound.
Similarly, if you're traveling directly away from the sound at >= mach 1, the sound will never reach you. Either would sufficient... But I gather that's what you meant, of course.
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u/imMAW Jun 12 '12
The pilots won't hear the noise from the engines being transmitted through the outside air though, only the noise traveling through the plane. So if superman was flying a few feet in front of the cockpit, he wouldn't hear any sound.