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 outage was a result of an unexpected hardware failure in Alaska's data centers and is not related to cybersecurity issues, the airline said.

U.S. carrier Alaska Airlines resumed operations late on Sunday after briefly grounding all of its flights for about three hours due to an IT outage, marking the second time it has halted its fleet in just over a year.