The article mentions that the 727 has a rear stairway that one can use to parachute out of the plane during flight, which the pilots did in this crash test. Random trivia: the famous hijacker DB Cooper picked a 727 for the same reason - he parachuted out the back of the plane with ransom money and was never seen again. For the interesting story, see http://en.wikipedia.org/wiki/D._B._Cooper