You will not only have to worry about the helicopter, but also the mobs of enemies that spawn around the stage. There are 3 attacks from the helicopter you will have to dodge. The chain gun, which will take off a chunk of life if you take too many hits. Slow missile takes more life off than the chain gun. Bombardment will happen when the helicopter swings around a building, this move is fatal as you will see it killed me in one attempt and took off 5 bars in another attempt.