Travel-technology provider Sabre said a glitch that prevented some airline travelers from checking in for flights on Tuesday was caused by a problem at one of its network suppliers.
Sabre spokeswoman Cassidy Smith said the issue affected airlines that connect with Sabre through CenturyLink's network.
Smith declined to identify the affected airlines. Some JetBlue customers complained they were unable to check in for flights.
CenturyLink spokeswoman Courtney Morton said activity during scheduled maintenance caused the disruption, which lasted for about two hours. She said the company was reviewing the incident to add safeguards that could reduce or eliminate future incidents.
FlightAware said 2,400 U.S. flights had been delayed by early evening on the East Coast, although it's unclear how many are related to the Sabre failure. About 24% of JetBlue flights were late, by far the highest percentage among the six largest U.S. carriers.
Sabre suffered a similar outage that affected several U.S. airlines on April 29.