CO-OP LEVEL 4
As you work your way through the level, you will get to the last part which is when you have a cut scene with the pilot. After that a vehicle with a turret will appear. Once you gain control of your guy, both of you run to the right where there will be a big crate. Make sure to stay in the shaded spots, and if you hurry, you won't get seen by the turret as it is appearing.
First, there is a guy to your left just standing next to the vehicle. Take him out. Depending on the position and spawn points of the other guys, they might or might not be in these locations. Your co-op partner should focus on the guy on top of the staircase to the right, while you take down the guy that is on the catwalk to your right looking towards the vehicle. If done correctly, you should have one guy left that is walking up the stairs, take him out.
As long as you did this correctly, have your co-op partner detonate a portable EMP, this will disable the turret for a short time. Run straight and hang a right past the stairs and into the open door in the building. There will be a guy in the building, melee him to get a mark and execute. After you take out the guy on your floor, go to the end of the room and there will be some stairs on your right, go up them, and waiting for you will be a guy, melee him as well.
Now to your right will be the dual EMP strike. This can be tricky, because the turret can shoot you. So one at a time get in position, if you or your partner goes down, no big deal.
Once the EMP is done, immediately go out the way you came in, down the stairs and hang a left to go to the door you came in by the outside stairs. At this final part, guys will continuously spawn, so don't bother picking them off.
As your running for the door, there are two open windows, you can try tossing a frag towards the center of the building, but it is not necessary.
Now that both you and your co-op partner are at the doorway, use your portable emp again and take off towards the plane. Continuously alternate every few seconds to ensure the enemies continue to stay stunned. Run up the opposite sites of the ramp and get behind the cover to raise the ramp.
Mission Completed. Hope this helped.