Here's a thought for a much later version: weather. Let me explain.
-variable wind speed and direction, with random changes (and a wind sock)
-varying temperatures at different altitudes.
-overcast skies, with varying cloud celings and tops.
-rain, yes rain, and rain effects, such as the droplets on your windscreen that blow off (see Flight Unlimited 2 for details)

-icing effects at high altitudes.
-wind sheer.
-wet runways
and at very least, mud spray for grass landings and ditches, and the tanks leave tracks n the mud.
my 2 cents.
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Lt. Col. Aaron "txace-" Giles of the 457th BG
"Fait Accompli"