American Airlines grounded all flights across the U.S. for most of Tuesday afternoon because of a computer outage. Flights resumed at 4:30 p.m. EDT. But the airline expects delays to linger throughout the evening. More than 720 flights were canceled, including 400 in Dallas and 200 in Chicago. More than 750 additional flights were delayed, according to flight tracking site FlightAware.

If you are stranded, here's what to do:

— To avoid a potentially long wait at the airport, think about canceling. American is offering free reservation changes and refunds for stranded passengers. If customers must travel 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, the airline announced. Flights are fuller than ever before, so it is unlikely there are many available seats on other carriers.

— To circumvent busy phone lines, Brian Kelly, founder of ThePointsGuy.com, suggests trying the airline's international customer service phone numbers or reaching out via Twitter — American's hashtag is (at)AmericanAir.

— Consider buying a one-day pass to the airline lounge. You can get away from the crowd and there are usually free drinks and small snacks. But the real benefit to the lounges is that the airline staffs them with some of its best and friendliest ticket agents. The lines inside will be much shorter and these agents are often able to find empty seats where nobody else can. One-day passes typically cost $50 per person. Up to three children under the age of 18 years of age may be admitted at no additional charge with an adult.

— Ask for a hotel voucher. The airline might be willing to pay for your room or at least get you a discounted "distressed traveler" rate.

— If customer service lines by the gates are too long, try to get a hotel discount voucher at baggage claim, suggests Gary Leff, co-founder of online frequent flier discussion site MilePoint. "When planes aren't flying there aren't long lines there and the baggage office can give those out," Leff said. Get a room early, he said, before they're gone. And worry about reimbursement from the airline later.

Finally, be nice.

"If this happened to me, I would take refuge in the American Airlines lounge and have a few drinks and wait because there is very little one can do," said George Hobica, founder of travel deal site Airfarewatchdog. "Keep calm and play nice. Screaming people do not get home faster than those who stay calm."

__

Scott Mayerowitz can be reached at http://twitter.com/GlobeTrotScott.