Federal officials halted Southwest Airlines flights from taking off on Tuesday.
By late morning on the East Coast, more than 1,500 Southwest flights had been delayed, accounting for well over half of all delays nationwide, according to FlightAware.
Southwest said on Twitter that it asked the Federal Aviation Administration to hold up departures because of intermittent" technical issues and hoped to resume flights as soon as possible.
The airline did not immediately respond to questions about the nature of the technical problem.
The FAA said only that Southwest requested the pause on flights, and referred questions to the Dallas-based airline.
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 and are being investigated by the Transportation Department.
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