Bill wrote:

The concept you are looking for is that there is less asymmetry
when you are higher in altitude.

Well yes, less engine power - less asymmetry (in a non-centerline-thrust
multi-engine aircraft, but for everything else, this discussion is moot
anyway).

Unless it's a turbocharged aircraft.

Obviously.

For 20 extra points, if you can get full sea level manifold pressure
in a TC
airplane, does Vmc decrease with an increase in altitude?

I'm a bit out my depth here, but let me think. It would stay the same if the
engine thrust is constant. That implies two things:
- Constant engine power (which we more or less have, thanks to the
turbocharger)
- Constant prop efficiency. I do not know about that.

So, it really depends on what propellers do at altitude. If they do not
decrease in efficiency, Vmc (indicated) would be constant, if they do
decrease, it would sink (though less dramatically than a
not-turbocharged/normalized aircraft).

However, once we get so high that the prop tips start going supersonic at
normal operating speed (Mach 1 decreases with altitude), we dramatically
loose prop efficiency, so at least at that point, Vmc will start to sink.

So, then. Show me the answer sheet.