Follow the president, listen to the talk and then head to the far side of the conference room. Keep some distance from the door and once you've brought your gun back up, kill the enemies here. Take their weapons so you have something more powerful than a pistol and head out into the hall. Walk into the next room and take out an enemy or two. When you try to advance, something interesting will happen. Just because you are airborne doesn't mean you can't shoot so take out whatever enemies you can. Once they are clear, you'll be back on your feet. Head down the stairs.
Turn around and head through the left door into the next room. Make sure you check right just as you enters the room to find an enemy waiting to ambush on the right door. Take him out and clear the room. Head up into the next room. Make your way slowly through the command area and into a small cargo room where you'll find four enemies and the President's daughter. Clear them out from a distance and move forward.
Soon someone will open the far door to the room. Head into the passenger section, try and kill a few enemies and then watch the plane get torn apart. Someone will help you up, follow him outside to find the President's daughter, and then set out to find the President. Follow him until you get close to the hanger. Move up the right side towards the jeeps. Use grenades on the jeeps to try and kill enemies as they are exiting. Watch out for gunners in the jeeps. Keep moving forward and the head right into the woods but watch out for the group of five enemies between you and the forest.
Get through them and kill the enemies further ahead by the jeep. Head forward to find the president. A chopper will put down nearby. Go open the door for the President and Mission... failed?

