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 temporarily grounded on Sunday.Thousands of passengers have been affected by knock-on delays and cancellations continuing into Monday as the airline scrambles to resume service.

Alaska Airlines warned of more flight disruptions on Monday after an unexpected failure of a critical piece of hardware at its data centers late Sunday forced it to halt all flights for about three hours.