Updated at 12:09 p.m. ET

Thousands of travelers on some of the largest U.S. airlines endured long waits Monday morning, as their flights were delayed owing to a contractor's computer outage. The technical problem forced Southwest Airlines, which had some of the biggest issues, to shut down all U.S. flights for about 40 minutes Monday.

"As of 9 a.m. Eastern Time, more than 600 Southwest flights today had been delayed," NPR's David Schaper reports. "United says about 150 flights with its regional carriers were affected; American and Delta also say a couple of dozen flights on its regional carriers were affected."

The delay hit Southwest shortly after 7 a.m. ET, forcing the ground stop that lasted until 7:45 a.m. The FAA announced at 8:30 a.m. that the "issue has been resolved." But by then, the delays were already mounting.

"Several U.S. airlines are experiencing computer issues this morning," the Federal Aviation Administration said on Twitter, asking passengers to check on their flight's status with their airlines. The agency reminded readers — some of them, no doubt, frustrated passengers whose planes had not taken off — that it does not control flight cancellations.

Southwest said it was a third-party vendor's computer outage that affected "data used in flight planning."

That vendor is AeroData, a company that lets airlines plan the weight and balance of their aircraft for safety purposes, along with other flight planning systems, Southwest said in an email to NPR.

AeroData's customers include Southwest, American, Delta, United and JetBlue — all airlines that reported delays Monday.

AeroData's system "is the last application used by pilots before the aircraft entry door is closed prior to takeoff," according to a 2017 company profile by data management company VMware. "As a result, just five minutes of system downtime can result in over 100 delayed flights and loss of revenue."

Major delays were reported at a number of airports Monday, from Phoenix to New Orleans and from Atlanta to New York and Chicago, according to Flightradar24. For affected airlines, the early disruption sent ripples through their flights Monday morning.

As they apologized to travelers, the carriers also said the situation was beyond their control.

"The AeroData system is coming back slowly," American Airlines said via Twitter, adding that further departure delays would likely be necessary Monday.

The technical problems added to weather-related safety concerns at a number of airports; the FAA said high winds also could lead to delays in Boston, Chicago, New York and Philadelphia.

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