Delta Air Lines said Tuesday that some computer systems are still working slowly more than a day after an outage crippled the airline and led to more than 1,500 canceled flights.

The system the airline uses to check in and board passengers and also dispatch its planes is still sluggish, said Delta's Chief Operating Officer Gil West.

He offered Delta's most detailed explanation yet of what happened Monday to trigger the global computer outage: A critical piece of equipment failed at the airline's Atlanta headquarters, causing a loss of power, and key systems and equipment did not switch over to backups as designed.

Delta passengers endured hundreds more canceled and delayed flights Tuesday as the carrier slogged through day two of its recovery from the meltdown.

At midafternoon, the airline said it had canceled about 530 flights as it moved planes and crews to "reset" its operation. More than 1,800 other Delta flights had been delayed, according to tracking service FlightStats Inc.

Transportation Secretary Anthony Foxx's office said the government was talking to Delta about technical issues surrounding the outage, but gave no specifics.

The Transportation Department said it made sure Delta provided information about customer refunds on its website and was reviewing the consumer complaints that it had received.

Delta's hub in Atlanta was the epicenter of problem flights. Debbie McGarry left Switzerland on Monday and was still stuck Tuesday at the Atlanta airport, far from her Arizona home. Hopes of getting on a plane were raised and dashed overnight. By 3 a.m., passengers were getting irate.

"Some of the men were yelling," she said. "I thought there might be a fistfight."

Tuesday's disruptions followed about 1,000 cancelations and 2,800 delayed flights on Monday. The airline's computer systems were back online after a few hours Monday, but the ripple effects lingered.

"We are still operating in recovery mode," Dave Holtz, senior vice president of operations, said on Tuesday.

Delta extended a travel-waiver policy to help stranded passengers rearrange their travel plans. And it offered refunds and $200 in travel vouchers to people whose flights were canceled or delayed at least three hours.

Delta's challenge Tuesday was to find enough seats on planes during the busy summer vacation season to accommodate the tens of thousands of passengers whose flights were scrubbed.

Airlines in general have been packing more people in each plane, so when a major carrier has a technology crash it's harder to find seats for the waylaid. Last month, the average Delta flight was 87 percent full.

Confusion among passengers Monday was compounded as Delta's flight-status updates crashed as well. Instead of staying home or poolside at a hotel until the airline could fix the mess, many passengers learned about the gridlock only after they reached the airport.

They were stuck.

A spokesman for the local electric company, Georgia Power, said the problem started with a piece of Delta equipment called a switchgear, which direct flows within a power system. No other customers lost power, he said.

Airlines depend on huge, overlapping and complicated systems to operate flights, ticketing, boarding, airport kiosks, websites and mobile phone apps. Even brief outages can now snarl traffic and, as the Delta incident shows, those problems can go global in seconds.

Last month, Southwest Airlines canceled more than 2,000 flights over four days after an outage that it blamed on a faulty network router. United Airlines and American Airlines both suffered outages last year -- United has struggled with several meltdowns since combining technology systems with merger partner Continental Airlines.