Southwest Airlines have revealed the reason behind a US-wide grounding of their entire fleet.
The airline's planes were stopped from taking off nationwide for what the airline initially called an "intermittent technology issue", causing more than 1,500 flight delays.
Passengers were left fuming after being told they could be waiting six hours for take off but luckily it proved far shorter.
Southwest and the Federal Aviation Administration said by late morning on the East Coast that the pause had been lifted.
Now the airline company has said they have resumed operations after the grounding caused by "connection issues resulting from a firewall failure."
The delays on Tuesday came just four months after the carrier suffered a meltdown over the Christmas travel rush.
The full statement from Southwest read: "Southwest has resumed operations after temporarily pausing flight activity this morning to work through data connection issues resulting from a firewall failure.
"Early this morning, a vendor-supplied firewall went down and connection to some operational data was unexpectedly lost. Southwest Teams worked quickly to minimise flight disruptions.
"We ask that travellers use Southwest.com to check flight status or visit a Southwest Airlines Customer Service Agent at the airport for assistance with travel needs. We appreciate the patience of our Customers and Employees during this morning’s brief disruption."
By late morning on the East Coast, Southwest accounted for well over half of all delays nationwide, but the airline had cancelled fewer than a dozen flights, according to FlightAware.
In December, Southwest cancelled 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.
Rardi Raad took to Twitter to reveal his flight was told it could be up to six hours before he's in the air.
He posted a video of him on the plane, writing: "Me two in Nashville! The flight deck told us it will take up to 6 hours.
"All planes that landed like ours have no gate to go to because the planes at the gate can’t move. SouthwestAir needs to do way better than it does."
Shawn Everitt, who is stuck on a plane in Nashville, revealed the passengers have been told to exit and wait in the airport while they wait for more information.
He told The Mirror: "Everyone is pretty upset. Sounds like we are getting off the plane finally to wait in the airport. The captain has not given any info on the situation."
Shawn previously said he had been sat waiting for thirty minutes with the engines off before being told what was happening.
Disgruntled passenger Kevin Jenkins said he was also stuck at the gate in Orlando after being told by the airline his flight cannot take off.
He tweeted: "Not another ground stop. Stuck at the gate in Orlando delaying our vacation. We just went through this exercise in December. My 11 year-old can probably fix the computer system."
