Richard Branson plans to send one of his 747-400 planes across the Channel between London and Amsterdam on a mix of 20 percent mystery biofuel and 80 percent conventional jet fuel.
The test flight will mark the first time a conventional airliner flies on any amount of biofuel, though the exact biofuel will not be named by Virgin anytime soon. Clues include: sustainable (i.e. not palm oil), won't compete with food (i.e. not soy or canola), and won't deplete fresh water resources (i.e. is already being grown with wastewater or soon will be.)
Not a lot of fuels presently available fit that bill: algae springs to mind as a feedstock as does UOP's "green diesel", as outlined in my new web feature on the subject.
But the flight itself will mark an epochal change in airplane fuel. The U.S. Air Force is flying on reformed fossil fuels (coal to liquid) and a smaller jet has flown on 100 percent biodiesel. The challenge is not the flight itself, it's incorporating this mystery biofuel into the entire air travel infrastructure.