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.
grunt soldier's achievement guide
this guy helped me a lot, if you ask nicely he will add your GT.