The airline confirmed that the failure of a third-party piece of hardware grounded flights, underscoring the fact that even systems that are multiply-redundant can go down.

"At approximately 8 p.m. Pacific on Sunday, Alaska Airlines experienced an IT outage that’s impacting our operations. We requested a temporary, system-wide ground stop for Alaska and Horizon Air flights until the issue is resolved," the airline said in a statement Sunday evening. The airline said it resumed operations at about 11 p.m. PT.

Alaska Airlines IT outage grounded all flights nationwide Sunday night. Find out what went wrong, who was affected, and what it means for travelers.