Steve Fosset hopes to soar into the record books with the first non-step jet flight around the world.
Virgin GlobalFlyer took to the skies from Salina in Kansas, US, at 0050GMT this morning.
There is little margin for error with bad weather conditions alreadly having delayed the flight by weeks.
The hardest challenge will be to safely manouver the single jet engine aircraft, which is loaded with more than four times its own weight in fuel for the challenge.
The route for the circumnavigation bid was changed at the last minute. The jet will now fly over North Africa instead of Europe because winds have shifted south.
It took GlobalFlyer about two hours to get to an initial altitude of 11.8km (39,000ft) before climbing at just 2.4m (eight feet) per minute to reach its cruising altitude of 15km (49,000ft).
The 1,522-kg (3,350lbs) single-engine aircraft is carrying nearly 8,636kg (19,000lbs) of fuel in 13 tanks for the approximately 37,000km (23,000-mile) journey at altitudes as high as high as 15,800m (52,000ft).
Its progress around the world is being tracked live on the GlobalFlyer website.
Andrew Zilouf
Virgin Solo Non-Stop Flight Run
US adventurer Steve Fossett aims to be the first man to fly a jet non-stop around the world.
