Hundreds of Alaska Airlines flights and thousands of passengers’ travel plans were disrupted over the weekend and well into Monday following a “significant IT outage” that resulted in the grounding of planes for about three hours.

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.

The failure, in the airline’s computer network, forced it to ground flights Sunday night for about three hours. The outage, tied to third-party equipment, yielded about 200 cancelled flights. A replacement is underway.