Southwest Airlines restarted flights in mid-morning on April 18 after an outage of around an hour due to problems with its IT systems.
"We've resumed operations this morning following a pause in service", the carrier said on its social media pages at around 1700 hours UK time.
Earlier the Federal Aviation Administration (FAA) said the carrier had "experienced a technical issue with one of their internal systems".
The FAA said the pause was requested by Southwest and advised people to contact the airline for information.
Around 1,700 departures were delayed by the outage.
"We know that delays can be frustrating and we regret your experience with us today", the carrier said in a social media post, replying to criticism from a passenger who said she was sitting onboard a delayed flight.
The carrier was forced to cancel almost 17,000 flights in December when an IT crash coincided with winter storms across swathes of the US.