Do not begin to push your front-end down to the transition (landing zone) unless you're sure the front tire is going to clear it. You should know or make the judgement call right at the apex of your height -- easier said than done. If you're not sure, bail FAST otherwise you'll land like this poor shmuck at http://www.big-boys.com/articles/bikewind.html. It's happened to everyone who's jumped proper doubles, and it hurts. That's actually how I broke my thumb in May.