Mission: Bio Lab
At the very end of the mission, you will enter a hovertank, and eventually make your way out of the base where enemy aircraft will begin to appear, both small and large helicopters.
At this point, you will have to keep your eye in the sky, and listen to your allies who will say "Warbird Incoming!" when they are near. If you see one, make sure you switch to your EMP, and hit it. Some helicopters take 2 shoots as well, so make sure it is downed before looking away. You will have to make progress forward for more aircraft to spawn. As you make your way to the end of the level, just continuously scan the sky for aircrafts and shoot them down immediately so they don't get away! If they do, you can try to reload the last checkpoint. After you shoot down 10 aircraft and reach the end of the area, the achievement should unlock. Go go too far forward, or it will end the level.