Updated 11/15/12 – 4:18 p.m.

CHICAGO (CBS) — A major computer outage at United Airlines delayed flights for thousands of travelers across the globe on Thursday, the third time this year a computer problem has hit the world’s largest airline.

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CBS 2’s Mike Puccinelli reports the two-hour outage left some passengers waiting several hours for a flight.

New Jersey resident Pat Marino said it was “very frustrating” for her and her husband, who waited more than three hours for a flight to Chicago.

“Some people got off the plane and left,” she said.

Chicago resident Thomas Hubbard chose to wait it out inside the plane at LaGuardia Airport.

“They told us this could be five minutes, it could be five hours. Turned out to be a little bit over two hours, and then we were eventually on our way,” he said.

United said things were back to normal by Thursday evening.

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“For about two hours this morning, an outage in one of our flight operations systems caused the delay of about 250 mainline United flights early today, with subsequent delays later,” United said in a written statement later in the day. “We found and corrected the error, and by mid-afternoon, systemwide on-time performance was approximately 80 percent. We apologize for the inconvenience this caused our customers. We are offering flexible flight-change and refund options for those customers affected today.”

Analysts said Thursday’s glitch was the third major computer outage for the Chicago-based airline since March.

“Here’s the problem: when the main system goes down, the backup system can’t always handle it,” said CBS 2 Travel Editor Peter Greenberg.

It’s a problem that’s been exacerbated since March, when United began using a computer program that previously was used by its merger partner Continental. Whatever the reason, some passengers said the outages might cause them to take a pass on united.

“If I could find another airline that was going where I was going, I might go somewhere else,” Marino said.

Hubbard said, “I’ll think about American next time, maybe.”

The first computer glitch happened in March, when United and Continental combined their reservation systems. It led to delays across the system, and problems for travelers trying to use airport check-in kiosks.

In August, another glitch led to delays for 580 flights, and United’s website was knocked out for two hours.

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