United Airlines grounded all of its domestic flights for two hours because of a computer glitch, leaving stranded passengers grumbling in airports across the US.

"The ground stop has been lifted.  We're working to get flights on their way.  We apologize for the inconvenience to our customers," the airline tweeted late on Sunday night in America.  

The US Federal Aviation Administration said that the Aircraft Communications Addressing and Reporting System (ACARS) had issues with low bandwidth.  No further explanation was immediately available, and United would refer to it only as "an IT issue."  International flights were not directly impacted, although travelers arriving on international flights had to wait for their domestic connections.  In all, 481 flights were delayed.

Airlines in the United States have had a rash of IT failures in the past two years.  In 2015, a computer issue prevented United from ticketing passengers and dispatching crews, disrupting travel for thousands of fliers.  Delta Air Lines took a US$100 million hit to sales in 2016 after a power-control module at the Atlanta command center caught fire in August, cutting power to computers.  Southwest Airlines halted flights the month before that because of issues with "multiple technology systems".