Searchers still hold out some hope for those aboard the private aircraft that seems to have flown on its own for hours before crashing off Jamaica Friday. But as the hours pass, the circumstances of what some are calling a “ghost flight” make that unlikely.

At this point, it’s not known exactly why an experienced pilot flying a high performance turboprop Socata TBM700 aircraft apparently lost consciousness, allowing the plane to continue on for some 1,700 miles. But clues are starting to emerge.

On a recording made by LiveATC, a website that monitors and posts air traffic control audio recordings, the pilot can be heard saying, "We need to descend down to about [18,000 feet]. We have an indication that's not correct in the plane." A controller replied, "Stand by."

After a pause, the controller told the pilot to fly at 25,000 feet. "We need to get lower," the pilot responded. "Working on that," the controller said. The pilot was cleared down to 20,000 feet, which he acknowledged. But he did not respond when the controller called again several minutes later.

This would seem to indicate that the aircraft was having a problem with its pressurization and oxygen system, which is critical to survival at high altitude. Unless the situation is quickly recognized and acted upon, hypoxia – oxygen deprivation that can lead to unconsciousness – can cause incapacitation and then death.

When the pilot – prominent Rochester, New York, real estate developer Larry Glazer – failed to respond to air traffic controllers, US Air Force fighter jets were launched from South Carolina and then Florida to track the aircraft as it headed for Cuban air space. The fighter pilots reported seeing the pilot slumped over. Apparently he lost consciousness without descending below 25,000 feet. Presumably, the aircraft continued to fly on autopilot until it ran out of fuel.

Jamaican authorities reported an oil slick. US Coast Guard ships and aircraft continued the search Saturday.

Mr. Glazer and his wife Jane Glazer (also a licensed pilot) had filed a flight plan from Rochester in upstate New York to Naples, Florida.

They were both well-known and highly-regarded in Rochester.

Mr. Glazer’s company, Buckingham Properties, owns more than 10 million square feet of real estate in downtown Rochester, including the Xerox Tower, the Bausch + Lomb building, and the Midtown Tower, according to the Democrat and Chronicle newspaper.

Jane Glazer started QCI Direct, a business that employs 100 people producing two national retail catalogs selling household and other products.

"The Glazers were innovative and generous people who were committed to revitalizing downtown Rochester and making the city they loved a better place for all,” Governor Andrew Cuomo said in a statement. “I offer my deepest condolences to the Glazers' family and friends during this difficult and trying time.”

Such occurrences are rare, although they do happen.

Last week, a pilot lost consciousness and his plane drifted into restricted airspace over Washington. Fighter jets were launched, staying with the small aircraft until it ran out of fuel and crashed into the Atlantic.

In 1999, the pilots of a Learjet carrying professional golfer Payne Stewart from Orlando, Florida, to Texas became unresponsive. The plane took a turn and wandered all the way to South Dakota before running out of fuel and crashing into a field west of Aberdeen. Stewart and five others on board were killed. An NTSB investigation blamed the accident on depressurization.

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Some speculate that Malaysia Airlines Flight 370 flew off course and disappeared when the pilots became incapacitated due to hypoxia.

This report includes material from the Associated Press.