A day after technology problems delayed hundreds of Southwest Airlines flights, the carrier’s operations were running more smoothly Monday.

Southwest spokesman Brad Hawkins said workers fixed a failed software application that had caused the problems. He did not provide more details or describe the application but said there was no indication that hackers were to blame.

The Dallas airline had been warning passengers early Monday morning to print boarding passes ahead of time and arrive at the airport two hours early. Airline officials said later that there was no longer a need to arrive early but that passengers might still want to print boarding passes at home in case of long lines at airport ticket counters.

On Sunday, Southwest suffered intermittent technical issues on its website, mobile app and in its phone centers and airport check-in systems. It used backup systems to manually check in some passengers.

The airline said that about 800 of its 3,355 scheduled flights were delayed at least 15 minutes Sunday. Passengers reported long lines at several airports including major hubs like Los Angeles International, where airport workers handed out water and provided shade canopies to travelers stuck in lines outside the terminal.

On Monday morning, Baltimore-Washington International Thurgood Marshall Airport tweeted that operations were returning to normal with few delays and shorter lines. Flight-tracking services indicated few if any Southwest delays by noon Eastern time.

Southwest Airlines Co. carries more than 100 million passengers a year within the United States, more than any other airline. On most days, its on-time performance is about average for a U.S. airline.

Through the first eight months of 2015, 78 percent of Southwest flights arrived on time, ranking seventh among the 13 largest airlines whose performance is reported by the U.S. Department of Transportation.

Airlines are large, complex organizations that are heavily dependent on technology, and even brief outages can strand thousands of passengers. United Airlines and American Airlines both experienced computer problems this summer. Both fixed the problems within a day and said that there was no indication of hacking.

(AP)