A hardware failure at an Alaska Airlines data center caused a system-wide “ground stop of flights” on Sunday night, the airline said. The airline has canceled more than 150 flights at various airports, including 64 Monday morning, with additional flight disruptions expected.

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.

Alaska Airlines says it has resumed operations early Monday morning, July 21, after an IT outage caused the airline to issue a temporary ground stop.