In a scene reminiscent of two embarrassing 2012 incidents, United Airlines is doing a lot of apologizing today after a problem with its reservation system has resulted in long lines at airports around the country.

The @United Twitter feed is currently littered with “very sorry” and “we are aware” responses to angry travelers who have been stuck in line for up to several hours at some airports.

“We are experiencing issues with our passenger service computer system,” United said in a statement to the Chicago Tribune. “We are working to resolve this as quickly as possible and apologize to our customers for any inconvenience.”

FlightAware.com currently says that 375 United flights (about 16%) have been delayed today. The big question is how many passengers are not making it to on-time flights because they can’t check in?

This situation reminds us of the problems United was having in the months after its merger with Continental Airlines.

Back in Aug. 2012, a system outage left travelers stranded at airports while the airline employees were helpless to do anything for them.

Then three months later, another crash shut down the nation’s largest airline’s system for a few hours.

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