Mark V. Rosenker, the acting chairman of the National Transportation Safety Board, confirmed the finding, saying that while the remains were “very little,” he believed that Mr. Fossett’s identity could be confirmed genetically.

“I believe the coroner will be able to do some work,” Mr. Rosenker said.

Sheriff John Anderson of Madera County said late Thursday that the remains were a small bone fragment that would be sent to the state’s Justice Department for forensic analysis.

Mr. Fossett’s aircraft was discovered Wednesday in a remote area of Inyo National Forest, about 120 miles south of the Nevada ranch where he departed on Sept. 3, 2007. Mr. Fossett, a renowned aviator, had said he was going on a brief flight but never returned, and the transponder on his aircraft did not send any location signals. At his wife’s request, Mr.Fossett, 63, was declared legally dead in February by a judge in Chicago.

Mr. Rosenker said parts of the transponder had been found, along with other pieces of Mr. Fossett’s plane, in a debris field some 150 feet wide and 400 feet long. Initial indications are that the plane hit a mountain, at an altitude of about 10,100 feet, and then burst into flame, investigators said. There was no sign the plane had been on fire before the crash, Mr. Rosenker said, but the plane’s engine was found 300 feet from the fuselage, which indicated an intense impact.

The wreckage lay about nine miles northwest of Mammoth Lakes, a popular ski village, and about 12 miles from the town’s airstrip. It is an area so remote that it required a 45-minute hike from the nearest path up steep hills, said the director of the Nevada Division of Emergency Management, Gary Derks, who visited the site and led the five-week search last fall for Mr. Fossett. About 30 investigators and other recovery personnel were on the scene, with volunteers and representatives from local sheriffs’ departments camping overnight in frigid temperatures to protect the scene.

The region where the plane wreckage was found had been flown over repeatedly during the search last year, but Mr. Derks said the area was dense, mountainous forest where something as small as a two-seat light aircraft would be easy to overlook.

On Thursday, searchers were still looking near the crash site with dogs trained to locate human remains, and expected to continue the search on Friday. But Mr. Derks said it was unlikely that any significant remains would be found.

“If they are, it’ll be a miracle,” he said, citing the passage of time, the rough winter and the presence of animals in the area.

Mr. Rosenker said weather would probably become a factor in the next 24 hours, as autumn’s first major Pacific rains moved onshore, with the expectation of high winds, freezing rain and even snow at the crash site. But investigators hoped to airlift all debris before that.

Mr. Fossett took off alone from the Flying-M Ranch in Yerington, Nev., in a blue-and-white Bellanca Citabria Super Decathlon, a single-engine two-seater. The ranch is a retreat for wealthy anglers and fliers. On Monday, a hiker, Preston Morrow, came across several of Mr. Fossett’s identification cards, money and a tattered fleece pullover in some bushes in the Mammoth Lakes region. Mr. Morrow reported his findings on Tuesday, and a search began on Wednesday, when a pilot spotted the wreckage.

Mr. Fossett held numerous world records. He was the first person to circumnavigate the world solo in a hot-air balloon and the first to fly a plane solo around the globe without refueling.

In a statement, Mr. Fossett’s wife, Peggy V. Fossett, thanked the searchers and the hiker who found his belongings.