Alaska Airlines has revealed that an "unexpected failure" of a critical piece of hardware caused an IT outage that led to its entire fleet being grounded.

Alaska Airlines stated that the IT outage resulted in a “temporary, system-wide ground stop for Alaska Airlines and Horizon Air flights” around 11 p.m. ET and lasted until 2 a.m. Monday, the airline wrote in a statement on X.

Alaska Airlines canceled over 150 flights — including 64 on Monday — after a critical IT hardware failure forced a system-wide ground stop late Sunday. The issue, unrelated to any cybersecurity incident,