HARTFORD, Conn. (AP) - An airline passenger said he had trouble breathing, and others felt ill, but the airline said Thursday that an inspection found no mechanical faults after the jet made an emergency landing in New York.

And while federal safety officials had no explanation for what happened on the aircraft on Wednesday, aviation experts said the flight crew did the right thing by quickly descending to 10,000 feet, an altitude with life-giving oxygen levels.

SkyWest Flight 5622, operating as United Express and carrying 75 passengers, left O'Hare airport in Chicago on Wednesday morning and was bound for Bradley International Airport near Hartford. The Embraer E170 began a steep, rapid descent from its cruising altitude of 37,000 feet after the crew declared an emergency and landed in Buffalo late Wednesday morning.

A U.S. official said the crew acted because of word of illness in the cabin but didn't report to controllers any problems with the aircraft.

"It's a big mystery," said the official, who was familiar with the incident but wasn't authorized to speak publicly and spoke on the condition of anonymity.

Passenger Larry Johnson, of Danbury, said it became difficult to breathe partway through the flight, though oxygen masks never dropped.

"They told us there was a leak in something and the pressurization was cutting short," he said. "They said if you got lightheaded, that was normal, but that we were going to have to descend and make an emergency landing."

He said several passengers were given oxygen.

"None of the air vents were working, and it was hard to breathe. You just felt that your chest was caving in, and then the plane descended so rapidly and that didn't help," Johnson said. "Me and my girlfriend, we were looking at each other. We were like, 'We don't feel good.' Everything was so bright, and when you blinked, you would see dots."

Inspections by airline mechanics and local authorities show "absolutely nothing wrong with the aircraft," SkyWest Inc. spokeswoman Marissa Snow said.

She said she had no confirmation that air wasn't coming from the vents in the cabin or that the air-handling system in the cabin was faulty.

For nearly eight minutes, the plane descended at a steep angle, dropping as fast as 7,000 feet per minute, the flight tracking service FlightAware said.