Lets assume you were able to walk on to the top of the plane without getting blown off. Lets also assume that you don't get cut in half by the tail of the plane when you somehow jump.
Then when you hit the ground, you would be going at roughly the same speed as the plane. So after your bones get mashed through your organs as you slam into the ground possibly rolling along depending at what angle you hit the ground at, your body would then be burnt up by the jet fuel from the burning wreck that your dead body bounces into.
In short you would actually be safer to stay inside the plane.
Just roll when you hit the ground. You'll be fine.
Un wibbly reply;
I dont think jumping would do anything unlesss you could jump higher than you were falling?
^No it's safest to lie flat on the ground to distribute the impact evenly.