Southwest Airlines said it was working Tuesday to restore normal operations after a technology-related issue interfered with flights for the second straight day. By midafternoon, the fourth-largest airline in the US had cancelled about 500 flights and delayed nearly 1,300 others. The combination of cancellations and delays affected about half of Southwest’s planned flights for the day.

The Federal Aviation Administration held up all Southwest departures for about 45 minutes while the company worked to fix a computer issue, an agency spokeswoman said.

Spokesman for Dallas-based Southwest said a problem with connectivity of the airline’s technology systems started around midday Tuesday.

A Southwest spokesman said the airline was in the process of resuming normal operations after a brief pause in flight activity resulting from intermittent performance issues with network connectivity Tuesday afternoon.

He said crews were working to limit flight disruptions, and urged customers to check their flight status Southwest’s website or seek help from the airline’s airport agents.

On Monday night, problems with a third-party weather data provider caused Southwest to delay about 1,500 flights. Delta Air Lines and Alaska Airlines reported separate technical problems that affected customers trying to book flights. Some Delta customers complained on Twitter that only first-class seats appeared for purchase on the airline’s website.

Airline technology systems are vulnerable to glitches and outages that sometimes snarl thousands of flights. In the last few years, a router failure crippled Southwest for days and Delta employees at one airport dragged out an old dot-matrix printer to make boarding passes. Airlines use huge, complicated IT systems that do everything from help operate flights to running mobile apps, and they are often overlaid with new programs.