Optimism that characterized last week's hunt for adventure aviator Steve Fossett began to wane Monday as the search for the missing man entered its second week.

"This search is big, it is frustrating and it is exhausting, physically and mentally," Maj. Cynthia Ryan of the Nevada Civil Air Patrol said.

Steve Fossett emerges from the GlobalFlyer airplane at the Salina Municipal Airport in Salina, Kan., on March 3, 2005 after successfully flying the craft solo around the world without refuelling.
(Charlie Riedel/Associated Press)

The quest involves 45 aircraft and has covered more than 44,000 square kilometres. Still, several potential sightings of the 63-year-old pilot or his single-engine plane in the rugged desert around the Sierra Nevada mountains have proved false. 

Fossett was last seen on Labour Day when he took off from the Hilton family ranch, about 130 kilometres southeast of Reno, in search of a site to try to break the land-speed record. He never returned from what was supposed to be a three-hour flight.

On Sunday, search efforts focused on an 80-kilometre radius around the private airstrip from which Fossett took off. Hopes grew when a helicopter and ground crew were sent to the scene of a possible sighting.

Within 30 minutes, though, rescuers confirmed the wreckage was "not the target aircraft."

"Once again you had your hopes raised and dashed just as we have," Ryan told reporters.

Rescue crews have found several undiscovered crash sites in their search for Fossett, some of them decades old.

Lyon County Undersheriff Joe Sanford said he had spoken with members of Fossett's family. Peggy Fossett remains at the Hilton family ranch where her husband was last seen.

"The mood is very sombre but very focused," Sanford said. "I can't imagine being on the receiving end of hope that continues to turn out to be unfounded or be something we were not aware of."

Fossett, a former commodities trader, was the first person to fly around the world alone in a balloon and broke the record for the longest non-stop flight in aviation history in 2006.

He flew a replica of a Vickers Vimy biplane across the Atlantic from St. John's to Ireland in 2005, recreating the first non-stop transatlantic flight, made in 1919.

He also sailed around the world, swam the English Channel and competed in a dog sled race.

With files from the Associated Press