MINDEN, Nev. &#8212 Nearly a week after record-setting aviator Steve Fossett disappeared, search leaders said Sunday they were still sure they would find him but acknowledged combing thousands of square miles has taken a toll on crews.

The aerial search, involving as many 45 aircraft surveying mountains and desert in western Nevada, still had produced no clue to Fossett’s whereabouts. Sunday was the sixth day of the operation.

“It’s not frustrating, but tiring,” Nevada National Guard Capt. April Conway said Sunday.

“Everybody’s waking up and saying ‘Hopefully, today’s the day,'” she told The Associated Press.

The 63-year-old adventurer has been missing since Labor Day, when he took off in a single-engine plane from an isolated ranch for a three-hour flight. He was said to be looking for dry lake beds where he could attempt to break the land speed record.

Civil Air Patrol pilots from throughout the West returned to the sky on Sunday morning, taking advantage of clear, cloudless weather with light wind.

The mood at Minden Airport, headquarters for the search-and-rescue operation, had dampened Sunday. Crew members declined to answer questions and referred all inquiries to Maj. Cynthia Ryan of the Nevada Civil Air Patrol, who would say only that pilots had received their assignments the night before.

In one sign that the effort has not produced as expected, nighttime flights using infrared scanners had been halted.

In addition to the civilian CAP planes, the National Guard has been assisting the search. As of Sunday, two of its helicopters were being based at the ranch 80 miles southeast of Reno where Fossett took off. The Flying M. Ranch, owned by hotel magnate Barron Hilton, has its own airstrip.

“The offer was made by Mr. Hilton yesterday,” Conway said. “Going by the logistics, such as refueling, it made a lot of sense.”

A number of private pilots involved in the search also have been using the ranch airstrip as a base.

Fossett is a skilled survivalist who has scaled some of the world’s highest peaks and survived several failed attempts to circle the globe in a balloon before finally succeeding.

It is that history that gives his friends and search-and-rescue team members hope that he is still alive.

They are searching an area of 17,000 square miles, about twice the size of New Jersey, an unforgiving land of steep mountain ranges and barren desert plateaus.

“This is one small airplane in one big area,” Nevada Gov. Jim Gibbons said Saturday during a visit to the operation’s headquarters at the Minden Airport. “I know every bit of how big the state of Nevada is, both from the ground and from the air. It is a challenge. It’s a big challenge.”

Search crews checked several tips that came from people who were near the California-Nevada border about the time Fossett was flying. None has panned out.

“So far, they remain four independent leads, four random pieces of a larger puzzle,” Ryan said. “If we can get some more leads to come in, hopefully one of them will match up with one of those others and we’ll have something significant to go after.”