An on-screen key layout for most used buttons would be nice as an overlay like PUBG has, just the basics like movement, switch weapon, etc. It could be adjustable like the on-screen speed and altitude area is.
I'd say default stuff like Engine, Flaps, Gear, Brakes, Throttle, RPM, numpad for default views, fire and switch weapon buttons. And of course have the ability to turn that menu off.