US Airways said it sent 20 extra workers to its Charlotte, North Carolina hub after a glitch in its self-service reservation system on Sunday forced thousands to wait in lines for up to three hours.
The airline said the wait to check in for flights was much shorter today, but it advised travelers to arrive at the airport two hours before their scheduled flights.
"We have all hands on deck right now," US Airways spokeswoman Michelle Mohr said, adding that it was unknown when the check-in process would be back to normal.
The carrier said the problem began early Sunday morning as it attempted to combine the reservations systems of the former America West Airlines and US Airways. The two carriers merged in 2005.
The work caused the self-service kiosks to fail, forcing passengers to stand in extraordinarily long lines and check in with ticket agents.
The disruption affected mainly US Airways travelers at the Charlotte-Douglas International Airport. But passengers at other East Coast airports were inconvenienced as well.
Thousands of travelers waited in the lines on Sunday and about 500 travelers in Charlotte missed their flights. Another 20 travelers in Pittsburgh also missed flights. Between 60% and 70% of US Airways' customers use the self-service kiosks.
Mohr said the airline has identified the problem and was correcting it.
US Airways has been blending operations of the former US Airways and America West since the merger. The carrier last year proposed a merger with bankrupt Delta Air Lines. The bid was rejected in January.