Rescuers called off the search for the aviator Steve Fossett last night, 17 days after his light aircraft disappeared over the Nevada desert.

After 474 flights covering 20,000 square miles, the Nevada Civil Air Patrol sent its aircraft back to base and the state’s National Guard helicopters were grounded, having found no trace of Fossett or his light aircraft.

Fossett’s wife Peggy continues to fund a private search involving eight light aircraft, but with hopes fading of finding him, legal experts gave warning of a potential legal battle over his multimillion-dollar estate.

Under the law in California, where Fossett lived, it could take at least five years before his family can have him declared dead. Without a death certificate his estate, estimated at over $50 million, cannot be administered.

Members of Fossett’s adventuring team in Chicago insisted last night that the private search would continue “until we find him”. They are being helped by internet users around the world who are examining live images of the Nevada terrain provided by Google. Brigadier General Amy Courter, of the Civil Air Patrol, said she had seen cases in which “people have survived much longer than this”. But her patrol is no longer actively looking for him.

Fossett, 63, the first person to circumnavigate the globe solo in a balloon and the holder of 115 aviation, speed and endurance records, disappeared on September 3 after taking off in a single-engine plane from a private airstrip to seek a site for a world land speed record attempt.

Dennis Belcher, the former head of the American Bar Association’s probate division, told The Times that if Mrs Fossett decided to have her husband declared dead, she could go to court and argue for an expedited ruling. The couple did not have any children.

But business partners or agents might have a financial interest in having him still legally alive, as income-generating agreements often terminate on death. He said court battles between parties who want a missing person declared dead and those who do not are common.

He cited a case he was recently involved in where a lawyer disappeared in his light aircraft over the sea. Neither his body nor the wreckage was ever found. A creditor wanted him declared dead as soon as possible. His family did not – his estate was declining in value because of a drop in the financial markets and they calculated that if they held off for several years, it would increase in value again. The parties spent 18 months in court. The man was eventually declared dead.

The massive search for Fossett also turned up six aircraft crash sites in the mountainous expanse of western Nevada and eastern California, with some dating back to the early 1960s.

For more than a week after the crash sites were reported, one family hoped that a 43-year mystery had been solved. Charles “Chazzie” Ogle’s single-engine plane disappeared over the Nevada desert in August 1964, and his son - who was 4 at the time – thought that the Fossett search might finally offer some answers. William Ogle, 47, said that the tragedy had “hung over me my whole life”, but last week his hopes were dashed.

Searchers said four of the wrecks were already on file with federal officials and dated from the past 30 years – although the planes’ pilots have yet to be identified.

A fifth “wreck” turned out to not be a crash site but merely debris. The sixth was dated to 1961 – three years before Mr Ogle, a multimillionaire land investor, disappeared. “We’re very sorry, but we believe now that Mr Ogle’s plane was not among the ones we’ve found,” said Major Ed Locke of the National Guard.

Conspiracy theories

Internet explanations for Fossett’s disappearance include:

—He was shot down by the US Air Force for straying too close to “Area 51” in Nevada where the Pentagon tests new aircraft

—He is not missing at all, but being used by the US Air Force as a cover story. While pretending to look for him, the military has actually been searching for a missing nuclear weapon

—He has been abducted to test-fly a UFO

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