Due to a widespread computer outage, Southwest Airlines experienced massive delays on Tuesday, and almost all flights out of its Chicago hub were grounded, CBS Chicago reported.
Southwest Airlines flights across the country were held up Wednesday while the airline worked to fix technology problems.
Spokesman Brad Hawkins said Southwest began having intermittent problems with several systems after an outage.
"We are now managing flight delays across our system, with a temporary ground stop in place for those flights that have not left the gate," Hawkins said in an emailed statement.
CBS News transportation correspondent Kris Van Cleave reported that the FAA said that the airline issued a nationwide ground stop for all departing flights.
Hawkins said that systems were gradually coming back, but that it might take time before the airline could resume normal operations.
CBS Chicago reported that automated check-in and baggage systems were down and passengers were being checked in by hand on paper tickets.
"Southwest Airlines began experiencing intermittent performance issues earlier this afternoon with multiple technology systems as a result of an outage," Southwest Airlines said in a statement to CBS News. "We are now managing flight delays across our system, with a temporary ground stop in place for those flights that have not left the gate. We apologize to our Customers whose travel plans are impacted."
Southwest also said on Twitter they are aware and investigating the current issues with their systems.
If you are seeing this image on the site you are in our waiting room. Don't refresh; we are working hard on a fix. pic.twitter.com/B1IDrDR2aC— Southwest Airlines (@SouthwestAir) July 20, 2016
Anxious customers tweeted to Southwest that they could not check in for flights. The airline's website wasn't working normally -- visitors couldn't buy tickets, check in for flights, or check their flight's status.
By about 4 p.m. Central time, Southwest had canceled 16 flights, more than any other U.S. carrier, and delayed about 150 others, according to tracking service FlightAware.com.
Airlines have sprawling, overlapping and complicated technology systems, and even brief outages can cause thousands of passengers to be stranded for hours.
Last October, an outage caused about 800 Southwest flights to be delayed and forced employees to issue tickets and boarding passes by hand. The airline blamed a software application, and it recovered in about a day. United Airlines and American Airlines both had computer problems last summer but fixed the problems within a day.
Dallas-based Southwest Airlines Co. carries more passengers within the United States than any airline. However, it is far smaller than American, Delta and United when international traffic is included.