QUOTE
the weight of your body (say 150 pounds), plus the impetus of your flying jump (say another 150 pounds), will drive your heels into your opponent's body with such terrific force that you will almost certainly kill him
...but it may get you a warning for excessive contact.
I've come across this before - there's some very good no-nonsense stuff in there from Mr Fairbairn. What strikes me though is the similarity to old style karate jutsu.