BC2's attack helicopter required nuanced keyboard controls (W/S for throttle, mouse for pitch/roll). Mapping throttle to analog triggers sounds great, but the game interprets the input as digital pulses. You will either spin uncontrollably or drop like a rock. Most controller users avoid flying.
The game will always display keyboard and mouse prompts on screen, regardless of your controller setup. Method 1: The Steam Input Solution (Recommended) battlefield bad company 2 pc controller support