sourabsansan

You are right. Now the solution. Dont go strait through the door, there is another way to beat them. Near the door to the helipad, there is a small way in the upright of the door. Now use your batarang,the lid will fall down. Go through that way. Only one guard will be there on the place where you reach. Now carefully get behind him and make a stealth.Don't worry. If you do it right, nobody will see you. Don't go to the hatch there is a broken place. Walk through there you will fall on a small place. Then grapple to the next point. Drop down from there and you will hold a vertical pipe. Look down using the right analog stick.You will see a window. Drop down and glide through the window. Now climb up the wooden things in your right side then glide to the vertical pipe so that you can hold it .Use the batarang to break the supports. There are chances for you to be spotted.So be carefull.Ok now you are ready to fight the enemies.Defeat them and interrogate the pilot.There is a grapple point under the helicopter.Grapple on the point when the helicopter is rising up.
I have completed all the levels in this game.If You have any doubts in the future missions, just ask me.
Thanks