PORTLAND, Ore. (KOIN) — The Federal Aviation Administration grounded all Alaska Airlines flights in the U.S. Wednesday morning after the airline said it discovered an issue with “the system that calculates our weight and balance.”

The problem occurred while performing a system upgrade, an Alaska Airlines representative said. That’s when they requested a ground stop from the FAA.

“Out of an abundance of caution, we requested a ground stop for all Alaska and Horizon flights, which was instituted at approximately 7:30am PT,” the company said in a statement.

The problem was “mitigated” and the ground stop was released an hour after it started.

The airline said delays were expected throughout the day as operations recovered.