Follow the vent until you are pulled out by a Brute. You'll need to use your combat skills to beat on the Brute until he falls down and then rush to the left side of the boxes and pull the parachute open. You won't be able to do much to avoid the boxes hurling at you and within no time you'll find yourself dangling off the back of the plane.
Climb up as you try to make your way back into the plane, pulling an enemy off, and get on your feet again. You need to make your way toward the nose of the plane, killing enemies off and watching out for the shifting boxes that can crush you. Eventually the plane will tear up and you'll be sucked out of the plane with no parachute. Luckily all the crates have parachutes, so grab on and pull that chute open life your life depends on it.