Go to the aircraft key assignment page and make sure your primary acceleration/deceleration is a key of your choice (W and S or the one you prefer). Right next to it you find the secondary option for acc/dec, put your joystick-axis in there. You should now be able to hit that key during flight to activate the booster. The other joystick-axis are on the primary side for me. I've assigned (via third-party software like Saitek's Programming Software or XPadder) the W-key to a joystick button. But for some reason it doesn't work in the MOD when double-tapping the joystick button. I've checked it with an editor and the button works, shows the "W" every time I pressed the joystick button. Maybe punkbuster or whatever denies access from third-party software. In BF2142 it was possible to create a macro which fired all missiles at the quickest possible interval with a single joystick click. Any ideas are welcome.