On the bridge you have to activate to get the tanks across, bring in a chopper and simply drive through the door to be there. You can proceed through the door and assist the tanks on the other side, or you can cross the bridge. To do this, aim your chopper for one of the tanks and turbo towards the bridge. When you get close, jump off. If you miss the tanks you will die. If done correctly, you will be on the bridge and alive.