American Airlines briefly grounded flights nationwide Tuesday due to a technical issue just as the Christmas travel season kicks into high gear.

American flights were cleared to fly by federal regulators about one hour after a national ground stop order was issued by federal regulators.

Just before 7 a.m. Eastern time, the FAA ordered all American Airlines flights grounded in the U.S. at the airline's request. American had reported a technical issue affecting its entire system with millions traveling for the holiday.

The ground stop, according to the time stamps on the FAA's orders, lasted exactly one hour.

American has not expanded on what technical issue grounded the flights.

Millions of travelers are expected to fly over the next 10 days. The TSA expects to screen 40 million passengers over the holidays and through January 2.

Many flights during the holidays are sold out, which makes cancellations even more disruptive than during slower periods. Even with just a brief outage, the cancellations have a cascading effect that can take days to clear up.