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Paul Beaty, Associated Press
Passengers wait in line at O'Hare International Airport in Chicago on Wednesday. American Airlines canceled more than 1,000 flights as it spent a second straight day inspecting the wiring on some of its jets. American estimated that more than 100,000 travelers were booked on the canceled flights. Many had to scramble to book new flights and were stranded at hotels far from home.

Business trips and vacations were disrupted for tens of thousands of travelers Wednesday as American Airlines canceled more than 1,000 flights — nearly half its schedule — to fix faulty wiring that could cause a short-circuit or even a fire and explosion.

It was the latest — and largest — in a wave of cancellations at major U.S. airlines that have caused long lines at ticket counters and made flying even more stressful than usual.

Executives at American said safety was never compromised, and they suggested the nation's biggest airline was the victim of suddenly stepped-up scrutiny by federal regulators.

American estimated that more than 100,000 travelers were booked on the canceled flights. Many had to scramble to book new flights and were stranded at hotels far from home.

The airline had already scrubbed 460 flights on Tuesday after federal inspectors found problems with wiring work done two weeks ago, during the first set of shutdowns.

Salt Lake City International Airport is not an American Airlines hub and with only seven daily flights, the impact Wednesday was minimal.

"It's been kind of a rolling target all day," said airport spokeswoman Barbara Gann. "We've had only two flights gone out, of the seven. More importantly, it looks like all the flights are canceled for tomorrow (today). We're getting our information from the Internet, but it looks like it's rolling into tomorrow, and maybe in a larger way than it was today."

Perhaps about 200 people throughout the day streamed through Salt Lake's American Airlines ticket counter, where employees set up a table offering snacks and water for those waiting to be booked on other flights, TSA agents said. A few waiting passengers were given gate area passes so they could access restaurants. Crowds were never unmanageable, and had dissipated by about 4:15 p.m., they said.

While things went smoothly, "there were people obviously distressed," one agent said. "There were a lot of not happy campers."

It was likely that American was both rebooking customers for later American flights or working to get passengers to their destinations by working with other airlines, Gann said.

"There was a little line for a while at one point today, but with the number of people involved with this, it hasn't built," she said. "I don't know if they're calling people in advance or if people are checking in advance with the Internet or the company before they come, but we haven't had a large number of people stranded."

A top executive said the cancellations would be a "significant" cost to American, and shares of parent AMR Corp. fell 11.1 percent, down $1.15 to $9.17.

The issue stems from an order that the Federal Aviation Administration gave airlines in September 2006 — and gave airlines until last month to meet — about the bundling of wires in the auxiliary hydraulic systems of MD-80 aircraft. The fear is that improperly bundled wires could rub, leading to an electrical short or even fire. However, no serious incidents have been blamed on the bundles, the FAA said.

Gann said she was unsure how many of the Salt Lake flights used MD-80 aircraft.

American officials thought they had fixed the problem last month. But this week, FAA inspectors found problems with the work done on more than a dozen planes. American said it had no choice but to ground all 300 of its MD-80s to deal with the wiring bundles.

American operates about 2,200 daily flights, more than one-third with MD-80s. Nearly half the cancellations were concentrated at two airports, in Dallas and Chicago.

At New York's LaGuardia Airport on Wednesday, hundreds of passengers stood in check-in lines or milled about, using cell phones to get updates on their flights. The airline offered free doughnuts, coffee and orange juice, but there were few takers.

"They should be able to predict these kinds of things," said Laura Goodman, whose flight home to Dallas was canceled. She said would miss an important meeting because the airline couldn't rebook her until today.

American's cancellations came after similar delays at Southwest, Delta and United. Last week, hundreds of travelers were marooned when Aloha Airlines and ATA Airlines shut down and filed for bankruptcy protection.

Alaska Airlines said Wednesday it canceled 14 flights to inspect the wiring on its nine MD-80s.

For travelers, the bad news might not be over. Daniel Garton, American's executive vice president, said flights would be canceled today — he said it was too early to say how many — and possibly on Friday, too.

A return to normal operations depends on how quickly mechanics can inspect and fix the wire bundles. As of Wednesday morning, only 30 MD-80s had been cleared to fly by the FAA.

Garton acknowledged that the bundling of wires had not met FAA standards, but he said "these were not huge errors" and posed no threat to safety. He said the agency used to give airlines "latitude" in interpreting safety regulations, but no longer.

The FAA began looking more closely at airlines' compliance with safety directives in recent weeks, after it was criticized for letting Southwest operate planes that had missed inspections for cracked fuselages.

In the past few weeks, the FAA levied a $10.2 million penalty against Southwest and conducted new inspections at all U.S. airlines, leading to flight cancellations at Southwest, Delta and United.

FAA spokeswoman Diane Spitaliere said inspectors found problems with the wiring bundles on 15 of 19 American MD-80s that it checked this week.

The 2006 safety order from the FAA directs airlines in how to pack and stow wiring to a hydraulic pump in the wheel well to prevent the wires from rubbing together. According to the FAA, shorted wires could ignite fuel vapors and cause a fuel-tank explosion that could destroy a plane.

Contributing: Brice Wallace, Deseret Morning News.