US aviator Steve Fossett has taken off from Cape Canaveral, Florida, in an attempt to make the longest non-stop flight in his Virgin GlobalFlyer plane.
His journey will take him around the world once and across the Atlantic twice, landing in Kent, UK.
If the 61-year-old makes it, he will eclipse a record set by Dick Rutan and Jeana Yeager in 1986.
On Tuesday, the three-day non-stop trip around the world was postponed because of a fuel leak and unfavourable winds.
Fossett began his trip from Nasa's Kennedy Space Center at about 1220 GMT (0720 local time), and plans to cover 41,978km (26,084 miles) in 80 hours.
The aviator already holds the record for flying solo around the globe in a balloon and for being the first person to circle the globe solo in a plane without stopping or refuelling.
That flight, in March 2005, was also in GlobalFlyer and lasted 67 hours. It was also hampered by a different problem of fuel leaking from the aircraft.
Mr Fossett circled the globe solo in GlobalFlyer last March
He will aim to break by 1,126 km (700 miles) the non-stop distance record set in 1986 by Dick Rutan and Jeana Yeager in a nine-day flight.
Fossett has told reporters that it remains to be seen whether the fuel venting problem experienced by the plane will reoccur on this flight.
After taking off from Florida, he will fly over the Atlantic, cross Africa, Saudi Arabia, India, China, Japan, the Pacific Ocean, Mexico, and the United States and then back over the Atlantic before landing at Kent International Airport outside London.
GlobalFlyer, a glider-like, graphite aircraft with a 35m (114ft) wing span, lifted off from a runway at Kennedy Space Center normally reserved for space shuttle landings.
It is the first experimental plane built by the private sector to take off from Cape Canaveral.
During his 80 hours in the air, Fossett will take power naps no longer than five minutes each and drink a steady diet of nutritional milkshakes.
His plane is equipped with a parachute pack holding a one-man raft and a satellite rescue beacon, just in case.