The Mile High Club isn't that hard if you memorize each section of the plane (how many enemies there are and where they come from), use flash bangs, and move forward as far into each section as you can. You'll notice your teammates are invincible, but only move as far as you do and can take out baddies with ease. In the section where the door blows out, move up and go prone behind the table on the left side. Your teammates will move up and take out everyone coming down the stairs. Once you're up the stairs, it's hide behind the middle barrier (shoot through it first) while you teammates move forward, go grab the flashes in the next room, throw a few down the next hall and sprint like hell to the door. The worst part is f'ing up the head shot on the final guy. I got to the final guy 3 times until I finally got it. MHC is easily the one achievement I was most happy/relieved to see pop.