Okay so this ones fairly easy to get with or without a friend, but if your having trouble getting it then this is the guide for you.

Campaign: Swamp Fever
Level 2: The Swamp

Co-Op: If your playing co op with one or four friends, have one friend go out and open the airplanes door, while the ones seeking the achievement are staying in the safe room at the beginning of the chapter.

Single Player: I got this one easy, all you have to do is camp between the rows at the far end of the plane, by the window and let the A.I kill all the zombies and of course, it pops, and voila achievement.

I hope this helps you guys, feel free to post or ask any questions you may have.