An extensive search has been launched for record-breaking US adventurer Steve Fossett, who went missing in his aeroplane in the Nevada desert.
Fossett has clocked up more miles than any other pilot in history
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 13 planes were searching for the 63-year-old.
The authorities were alerted when Mr Fossett's family reported him missing after he failed to return from a trip which should have lasted just a few hours.
Maj Ryan said conditions for Mr Fossett's flight had been "optimal", with calm to light winds.
"The Civil Air Patrol is looking for him. One problem is he doesn't appear to have filed a flight plan," Federal Aviation Administration spokesman Ian 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.
Officials say Mr Fossett's plane was fitted with an electronic beacon which can be picked up by satellites, but have refused to comment on whether any signal has been located.
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 a forthcoming 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.
The search was later suspended for the night.
Mr Fossett reportedly took off from an airstrip near Yerington, Nevada, owned by William Barron Hilton, heir and co-chairman of the Hilton Hotel chain.
Since the 1960s the airstrip has been regarded as a Mecca for pilots and a popular haunt for world class aviators and astronauts alike.
SOME OF FOSSETT'S RECORDS
1998/2002: Long-distance for solo ballooning
2001/2002: Duration for solo ballooning
2002: First solo round-the-world balloon flight
First balloon crossings of Asia, Africa, Europe, South America, South Atlantic, South Pacific, Indian Oceans
Seven fastest speed sailing titles
13 World Sailing Speed Record Council titles
2001: Fastest transatlantic sailing
2004: Fastest round-the-world sailing
Round-the-world titles for medium airplanes
US trans-continental titles for non-military aircraft
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.