Oh, I know how to do that, I looked up grunt soldier's mile high club achievement tutorial.
basically you can only reload 2 times on the second floor, do not waste time grabbing other weapons, it is bad.
first dash up to the bathroom and knife the man, then run straight ahead into the conference room and head shot the shotgunner there. beware, start shooting him after you knife the bathroom dude. once you do, go into crouch and flashbang the room the shot gunner was in, and 4 guys who run in will be flashbanged, shoot through the seats and knife whoever is left. the goto the next room and hide behind the seats, reload now, and wait for the side of the plane to be ripped out, move foreward, shoot through the seats again, reload and head to the second floor. and at this point it is up to luck... you can only reload 1 time in the second floor otherwise you will not make it.
You have to sit through the credits to open up this level. As far as I know this mission isn't related to the plot in any way. Kill the terrorists as you proceed towards the front of the plane. You have 1 1/2 minutes to find the hostage. Note that you can shoot through seats to hit the terrorists behind, but the same is also true for yourself. Go up the stairs at the front and turn around, killing the opposition. Aim down the sights of your pistol and kill the terrorist before evacuating the plane by jumping out.
its 1 minute on veteran, and 4 shots kill you or one shot from shot gun.
And Zombie Genocidist on L4D. You have to play a long time to get it.
here is what my friends and I did. we got a car and drove over zombies in the sewer. We each played 30 minutes and let the other person go for a bit, until we got the achievement LoL. its good to have friends.