AA promises near-normal operation Wednesday

American Airlines has resumed at least some flights after a computer glitch forced it to ground all of its flights for several hours Tuesday.

A slow resumption of flights came shortly after 5 p.m. ET, but American warned "we expect continued flight delays and cancellations throughout the remainder of the day."

American Airlines is promising to run a near-normal operation on Wednesday, according to AP.

More than 730 flights on American and regional affiliate American Eagle had been canceled as of 4:15 p.m. ET, according to flight-tracking service FlightAware. An additional 738 American flights were delayed today because of the glitch.

"This is a major outage for American and is the longest flight disruption as a result of a failure of an airline's back-end technology in recent history," FlightAware CEO Daniel Baker says to Today in the Sky. "It is likely to affect over 125,000 travelers today and tomorrow. United had a few similar outages last year, some as a result of the Continental/United merger and related technology fallout, but none were nearly as long as this" problem, which lasted more than five hours.

FlightAware says most of the AA's delays and cancellations have come on flights to or from AA's main hub at Dallas/Fort Worth, though Chicago O'Hare, Miami and New York LaGuardia had also seen significant problems.

Even once flights resume, Baker estimated that about 800 additional American and American Eagle flights "will be indirectly impacted by planes and crews out of place."

At American, the airline encouraged fliers with flexible schedules to put off travel.

"If your travel plans are flexible, there will be no charge if you would like to change your reservation and we will provide full refunds if your travel plans are not flexible," Huguely said in a statement to Today in the Sky.

American provided additional information on how it planned to accommodate waylaid fliers. In a statement, the airline said:

• If customers must travel today and are already at the airport, they can rebook on another airline by visiting an American Airlines agent or by going to the other airline's ticket counter with their electronic ticket number. If customers secure a flight on another airline, then American will refund the cost of the ticket and reimburse customers for any fare difference between the original fare and the new ticket.

• If customers must travel today and are not yet at the airport, they can rebook through American Airlines reservations or through another carrier and American will honor the fare difference.

• If a customer chooses not to travel today, there will be no charge for reservation changes or a full refund will be provided.

Earlier in the day however, reports and photos of long lines at American's check-in counters poured in from across the country via both social media and traditional news outlets.

At American's hub in Miami, The Miami Herald reports that landing AA flights had run out of available gates since none of the airline's departures were taking off.

A passenger on one of those flights — 66-year-old Richard Bell — tells the Herald he had been stuck on an AA flight arriving from Baltimore. He told the newspaper that the aircraft's engines were running and that the air conditioning was working. But he also said the flight's pilots come over the public address system to warn fliers that some other systems were not functioning.

"He mentioned the toilet specifically as a problem,'' Bell tells the Herald.

NBC 4 of Los Angeles showed a filled-to-the-brim seating area at one of American's gates at Los Angeles International, while the Los Angeles Times shows a number of Tweets from passengers affected by the disruption.

American had been having "intermittent " problems throughout the day, but announced at 2:38 p.m. ET that it was grounding all flights in an effort to resolve the problem.

American initially appeared to blame the crash on a crash of the Sabre reservations system. However, AA eventually backtracked, saying via Twitter that "the issue is (with) our ability to access our res system" and not with Sabre itself.

The carrier, the USA's third-biggest, first warned customers of the problems via Twitter at 12:30 p.m. ET.

"American's reservation system is experiencing intermittent outages," AA spokeswoman Andrea Huguely said in a 1:50 p.m. ET e-mail to Today in the Sky. "We're working to resolve the issue as quickly as we can. We apologize to our customers for any inconvenience."

Once the scale of the problems became evident, American requested a Federal Aviation Administration ground-top for flights on American and American Eagle.

Speaking to USA TODAY after a Senate hearing, FAA Administrator Michael Huerta said AA requested the ground stop based on their operations and concerns about the company's computers.

"It was requested on their end," Huerta said. "It was a problem with their computer system."

"They requested the ground stop based on their operational needs, based on their computer systems," Huerta said.

Contributing: Bart Jansen