Rescuers searching for missing U.S. adventurer Steve Fossett said flying conditions on Monday were optimal and Fossett had plenty of fuel onboard and was unlikely to have been performing any risky stunts.

Thirteen planes from the Civil Air Patrol, as well as ground crews, combed rugged, mountainous terrain on Tuesday, but had few clues about where the plane carrying the 63-year-old world record-holder might be.

At a news conference, Cynthia Ryan of the Civil Air Patrol said Fossett's single-engine Citabra Super Decathlon is a reliable, durable plane flown by many pilots in the region, and can be used to perform tricks.

"However I understand Mr. Fosset did not care for acrobatics so it's unlikely he would have been doing anything like that," Ryan told reporters.

"People of his experience and background sometimes like to go out and push the envelope a little, although I understand from his pilot he was a very conservative pilot."

Fossett, a millionaire entrepreneur who holds land-speed and aviation flight records, was last seen Monday at 8:45 a.m. local time at a ranch south of Smith Valley in western Nevada.

He was taking off from hotelman Barron Hilton's Flying M Ranch, a private airstrip located about 112 kilometres southeast of Reno in the south end of the Smith Valley.

When Fossett didn't return at noon, as scheduled, the Flying M Ranch sent out its own search planes. Fossett was reported missing to the authorities on Monday evening when the search proved unsuccessful, Ryan said.

Rescuers searched for several hours Monday night using night vision technology, then all day Tuesday. Ryan said they were following up on electronic data, but had few concrete clues about Fossett's location. Still, they were not giving up hope.

"As far as we know so far it's still a rescue mission and until we have more information it will remain one," Ryan said.

Capt. Mike Glazer, of the Naval Air Station in Fallon, Nevada, told CTV Newsnet that the area where Fossett is believed to be missing is rugged and mountainous.

"One of the sites located out there is near Bridgeport, Calif., where the marine corps conducts their mountain warfare training centre," Glazer said.

He said rescuers have few hard clues about where Fossett may be, since he didn't file a flight plan prior to departure.

"Basically, he had talked to some friends before taking off and had given them a general route of flight, so that gave us some indication of where to search," Glazer said.

"Also, the air traffic control radar had a number of hits on different aircraft that may have been his, so that helped us to localize the search area."

The search is being coordinated by the U.S. Air Force's Rescue Co-ordination Center in Langley, Virginia.

Fossett is probably best known for setting five world records for non-stop circumnavigations of the globe.

He achieved the records using hot-air balloons, airplanes, gliders and sailboats.

Following are some of Fossett's aviation accomplishments:

• 1998/2002: Long distance record for solo hot-air ballooning
• 2001/2002: Duration record for solo hot-air ballooning
• 2002: First solo balloon flight around the world
• 2005: First solo nonstop and non-refueled circumnavigation of the world in a single engine jet airplane
• 2002: One of aviation's highest awards: the Gold Medal of the Federation Aeronatutique Internationale
• 2004: fastest sailing circumnavigation of the world
• Ten of 21 Glider Open awards