A plane flown by record-breaking US adventurer Steve Fossett is missing in the Nevada desert, US federal aviation officials have said.
Mr Fossett was reportedly last seen taking off from the private airfield at the Flying M Ranch near Yerington, Nevada, on Monday evening.
He was flying a blue and white single-engine Citabria plane.
A Civil Air Patrol spokeswoman, Major Cynthia Ryan, said a search for the 63-year-old was under way.
Federal Aviation Administration spokesman Ian Gregor said authorities had been alerted when a friend reported Mr Fossett missing.
"The Civil Air Patrol is looking for him. One problem is he
doesn't appear to have filed a flight plan," Mr Gregor told the Associated Press news agency.
Mr Gregor said the Air Force's Rescue Co-ordination Center in Langley, Virginia was overseeing the search.
"They are working on some leads, but they don't know where he is right now," he was quoted as saying.
Speaking to the BBC about the disappearance of his former crewmate and one-time ballooning rival, Virgin Atlantic President Sir Richard Branson said he was confident his friend would be found safe and well.
"Steve is a tough old boot. I suspect he is waiting by his plane right now for someone to pick him up," Mr Branson said.
"The ranch he took off from covers a huge area and Steve has had far tougher challenges to overcome in the past. Based on his track record, I feel confident we'll get some good news soon."
Mr Branson's spokesman said Mr Fossett was carrying four full tanks of fuel, and was searching for empty lake beds suitable for an upcoming attempt at the land speed record.
Trooper Chuck Allen from the Nevada Highway Patrol told the BBC that teams from neighbouring California were aiding the search.
"Several aircraft (are) flying many hundreds of square miles doing a very extensive grid search to try to locate this particular aircraft," he said.
Mr Fossett reportedly took off from the Flying M Ranch, near Yerington, Nevada - a private airstrip owned by William Barron Hilton, heir and co-chairman of the Hilton Hotel chain and grandfather to socialite Paris Hilton.
Mr Barron Hilton has had a passion for flying since his youth, in particular gliding, and he invites pilots who have completed the longest flights to the exclusive ranch to take advantage of its excellent local gliding and A-grade facilities and to meet fellow pilots.
Since the 1960s the Flying M has been regarded as a Mecca for pilots and a popular haunt for world class aviators and astronauts alike.
In 1981 Mr Barron Hilton founded the Barron Hilton Cup, a prestigious international competition for gliders.
Mr Fossett made his fortune in the American financial services industry, but he is best known for the impressive number of world records he has broken as a pilot, balloonist and sailor.
He has set 116 records in five different sports, more than 60 of which remain unbroken.
Last year Mr Fossett broke the world record for flying further than anyone else in history.
In March 2005, he became the first person to fly a plane solo around the world without refuelling.
And in 2002 he was the first person to fly a balloon around the world solo.
Poor guy, hope he's okay.http://news.bbc.co.uk/1/hi/world/americas/6978818.stm