Southwest Airlines Boeing 737 MAX-8 (Ashlee D. Smith/Southwest Airlines)

(AP) — Southwest Airlines planes were grounded nationwide for what the airline called an intermittent technology issue, causing more than 1,700 flight delays Tuesday just four months after the carrier suffered a meltdown over the Christmas travel rush.

The hold on departures was lifted by late morning, shortly after it was announced, according to Southwest and the Federal Aviation Administration, but not before traffic at airports from Denver to New York City backed up.

“Southwest has resumed operations after temporarily pausing flight activity this morning to work through data connection issues resulting from a firewall failure,” the Dallas airline said in a prepared statement. “Early this morning, a vendor-supplied firewall went down and connection to some operational data was unexpectedly lost.”

The airline urged customers to check on their flight status “and explore self-service options” for travel as the airline worked on restoring its operation.

By late morning on the East Coast, Southwest accounted for well over half of all delays nationwide, but the airline had canceled fewer than a dozen flights, according to FlightAware.

A FlightAware search showed no delays out of Fresno Yosemite International Airport.

Tuesday’s flight freeze was brief, but it added to the picture of an airline that has struggled more than most with technology issues. CEO Robert Jordan has embarked on a campaign to repair the airline’s damaged reputation.

In December, Southwest canceled nearly 17,000 flights over the Christmas holiday due to bad weather and its crew-scheduling system becoming overwhelmed. Those cancellations cost the airline more than $1 billion. The Transportation Department is investigating the breakdown.

The airline’s unions have said they warned management about problems with the crew-scheduling system after a previous meltdown in October 2021.

Southwest said last month it would add deicing equipment and increase staffing during winter weather that is cold enough to limit the amount of time that ground workers can stay outside.

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The Business Journal contributed to this report.