It certainly would be nice if external engine and plane sounds could be heard. I know everyone says that "you couldn't hear it anyway," but I think the sounds should be in the game.
I think all external sounds should be at real-life amplitudes, and then any closer ambient noises, such as your plane's engine, tank, etc. should drown out the rest from there. That way, if you are trying to sit silent you would be able to hear the things going on around you.
With all the talk about what realism should be, I think sounds should be on or near the top of the list.
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"Wing up, Get kills, Be happy"
Midnight
13th TAS