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.

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 Air Group Inc. continued to recover on Monday after temporarily grounding its entire fleet due to a data center equipment failure that affected several of the carrier’s key operating systems.