I think it'd be quite difficult to try and aim headfirst since I've heard SI kicks in when you're falling. You most likely will die? I suppose it could also be dependant on the terrain, if there's soft grass and dirt you might survive and if there are tall trees that break your fall, etc. If you can, I'd say concrete or a harder surface and/or landscape would be best? There's still always the chance of just crippling yourself and not passing though, but I suppose there's that chance for everything.