Wreckage found today in California has been identified as the aircraft piloted by adventurer Steve Fossett.
A pilot's licence and a second identification document featuring Fossett's details, which were found by a hiker, were also confirmed as authentic today, Madera County Sheriff John Anderson said.
Sir Richard Branson said he expects the body of his "great and extraordinary" friend to be found soon.
The NTSB said the crashed plane was found yesterday and a team of investigators were sent to California to investigate.
"The Bellanca 8KCAB (N240R) has been missing since September 3, 2007, when the pilot departed Yerington, Nevada, for a local flight," the statement said.
"The wreckage was located at about 10,000 feet of elevation in the Sierra Nevada Mountains in the vicinity of Mammoth Lakes, California."
The discovery came after a hiker found three identification cards bearing Fossett's name in a bush just west of Mammoth Lakes.
Preston Morrow said he found a Federal Aviation Administration identity card, a pilot's licence, a third ID and £558 in cash on Monday but saw no sign of a plane or of any human remains.
He handed the items to police yesterday after failing to contact Fossett's family directly.
Mammoth Lakes is around 90 miles south of hotel magnate Barron Hilton's Flying M Ranch where Fossett, 63, was last seen alive as he set off in the single-engine aircraft on 3 September last year.
Sir Richard, who backed some of Fossett's record attempts and unsuccessfully tried to circumnavigate the globe by balloon with him, said: "It looks very much like we're close to finding Steve.
"Hiker Preston Morrow needs to be thanked for alerting the authorities, helping them with satellite co-ordinates and being good enough to turn in the 1,000 dollars cash."
Until this week, no trace had been found of Fossett and there has been speculation that he faked his own death.
Sir Richard's statement added: "This should now lay to rest the frivolous stories about Steve and give everyone close to him the chance to pay the right tributes to a truly great and extraordinary man."
Virgin Atlantic, one of Sir Richard's companies, sponsored GlobalFlyer, the plane used by Fossett in 2005 to become the first person to fly a plane solo around the world without refuelling.
Sir Richard told Sky News: "It's likely he will be found in the next few days and they will be able to find out what went wrong.
"He was flying into a perilous mountain area - whether the engine gave out on him or whether he had a heart attack or some other medical problem, you don't know."
Fossett, who made millions as a commodities broker in Chicago, was looking for suitable sites to attempt a new landspeed record when he disappeared.
Sir Richard said Fossett had led "a most extraordinary life but died doing something quite mundane" and added that his friend's death would not put him off taking on dangerous challenges.
"I don't think what happened to Steve should deter people from pushing themselves. There's no question he would have wanted people to see what they were capable of and see if technology could be pushed further."
Andy Green, who lives in London, has held the landspeed record for 11 years and was helping Fossett prepare for his attempt to break it.
"I really want to know what happened to my friend Steve," RAF fighter pilot Mr Green said.
"His widow has found it very hard, as anyone would, when your husband of many years just disappears.
"For all of them, I'm hopeful that finally we will have some closure on this."
Don Cameron, of Cameron Balloons in Bristol, got to know Fossett when the firm made hot-air balloons for his record attempts, including the first solo non-stop round-the-world trip in 2002.
He said it was sad that a man who had survived crash-landing a balloon in shark-infested waters off Australia seemed to have died in a simple plane crash.
"He certainly knew how to fly an aeroplane. If they do find something, maybe the investigators will be able to figure out what happened.
"I think for his family it'll be better if they do know the truth and if they recover remains and can have a funeral.
"It's probably better than leaving it unknown although I don't think there was much doubt it was an air accident.
"I never believed for a moment all the stuff about him faking it. I never thought he was that sort of chap."
Mr Cameron added: "He was the opposite of the brash American. You could know him for years and suddenly discover things he'd done that were amazing.
"He was a great character. He was brave and had tremendous stamina."
Fossett was declared legally dead in February by Illinois judge Jeffery Malak.
Fossett's widow Peggy said in a statement yesterday that she hoped the search would locate her husband's remains and added: "I am grateful to all of those involved in this effort."
The hiker who found the documents which sparked the search near Mammoth Lakes, said he did not know who Mr Fossett was initially but a colleague recognised the name.
"It was just weird to find that much money in the backcountry, and the IDs," he said.
"My immediate thought was it was a hiker or backpacker's stuff, and a bear got to the stuff and took it away to look for food or whatever."
Mr Morrow said he returned to the scene with his wife and three friends on Tuesday and found a black Nautica pullover fleece in the same area but could not be sure it was linked.