As for chopper, planes should react to damages changing the way they fly.

Planes in this moment have only a HULL damage indicator, and doesn't react to damage in any way until they simply explode.

maybe should be added others damage indicators such as:

WINGS effects: visual vibration, difficulty to pitch and roll, stall on higher velocity, flaps stop working
FUEL effects as for chopper
TAIL effects: difficulty to yaw
ENGINE effects: engine with reduced power or stop working
GEAR effects: no gear so you have to land without it (should be possible at least on flat surfaces)