Updated 04/12/13 – 5:58 p.m.

CHICAGO (CBS) — Officials at O’Hare International Airport are saying a bit more about what caused lights to fail on two runways Thursday night, but have yet to determine an exact cause.

The failure occurred during a planned changeover from one power source to another, at about 9:30 p.m. The switch had to be done manually, and Aviation Department spokesman Gregg Cunningham said that took 10 minutes to complete.

At DePaul University’s Chaddick Institute, transportation expert and director Dr. Joseph Schweiterman told WBBM Newsradio’s Bob Roberts it is a potentially dangerous situation.

“You’ve got multiple systems to try to avoid this kind of outage,” he said. “It’s an embarrassment to the city. A couple of things go wrong and you could have a safety problem that’s a cause for concern.”

Schweiterman said lights going out as a jumbo jet lands, disorienting pilots, is the last thing O’Hare needs, He said it demands further investigation to determine what failed.

Officials at O’Hare said they are still trying to pinpoint where the failure occurred, but said it happened as power was being switched automatically from one source to another.

The failure occurred at about 9:30 p.m. Thursday, and affected runways 9-Left/27-Right and 9-Right/27-Left, said Aviation Dept. spokesman Gregg Cunningham. Both runways are on the north side of the airport.

As a result, he said, power had to be switched manually, a process that took about 10 minutes.

Karl Huff was coming in from San Diego when the runway lights went out.

“We kind of went in a holding pattern for about 20-25 minutes,” he said.

The power failure caused delays for more than half an hour to inbound flights. Since then, he said, the power has not failed and runway lights have been fully operational.

Cunningham called the outage “very unusual,” because of the airport’s redundant power systems.

During the outage, planes expecting to use those runways were forced to circle and wait for another runway to open up.

Aviation officials blamed unspecified “electrical problems,” and said “the traveling public was never at risk during the incident.”

CBS 2’s Mike Puccinelli reports some passengers were understanding about the mishap.

“Things happen. I mean, if you look at the Super Bowl game, when the lights went out, no one predicted that, but it did,” Lavert Daniel said.

Others were upset it was allowed to happen.

“That’s very concerning, I mean that concerns the passengers; the possibility of crash. I mean, that’s danger right there,” Joannah Atal said.

Monsurat Ragi was also concerned, and she knows something about power and what causes it to go out.

“I’m in the electrical distribution business, and we’re trying to figure out exactly how come the battery backup system didn’t work,” she said.

The number of flights delayed by the outage was not immediately available.

Flights Thursday also were delayed and/or cancelled because of low visibility, but Cunningham said the only delays Friday were because of the foul weather, now at east coast airports. In all, more than 180 flights were cancelled because of the weather.

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