This achievement isn't very difficult during normal play, however there is a simpler way obtain it. To get it normally I recommend playing in squads and allowing yourself to get kills while your team assists you. You have to knock the enemy down and someone has to finish them off for the kills to count. The easier way to pop this one is waiting on the plane until the end of its "route" and having it automatically eject you. There will be a handful of people not playing and you can find at least 4 in a couple of tries. I find this method is best done in solo.