(Reuters) – Major U.S. airlines including American Airlines (NASDAQ:), Delta Air Lines (NYSE:) and United Airlines (O:) grounded planes on Friday morning citing communications issues, less than an hour after Microsoft (NASDAQ:) resolved a cloud service outage that affected several low-cost carriers.
It wasn’t immediately clear whether the request to halt flights was related to the previous Microsoft cloud outage. In addition to American and Delta, UAL and Allegiant Air (O:) have also suspended flights.
The FAA did not immediately respond to Reuters’ request for comment.
Low-cost carriers Frontier Airlines (a subsidiary of Frontier Group Holdings), Allegiant and SunCountry previously reported disruptions affecting their operations. Frontier said late Thursday that it was in the process of resuming normal operations and that the grounding had been lifted.
Frontier previously said its operations were temporarily disrupted due to a “major Microsoft technology outage,” while SunCountry said its reservations and check-in facilities were impacted by a third-party vendor, though it did not name the company.
Transportation Secretary Pete Buttigieg said the department is monitoring Frontier Airlines’ flight cancellations and delays, adding that the agency will hold Frontier and all other airlines “to account for meeting the needs of our passengers.”
“Due to an issue with Microsoft Azure, the Allegiant website is currently unavailable,” Nevada-based Allegiant said in a statement to CNN. Allegiant did not immediately respond to a Reuters request for comment.
Frontier canceled 147 flights and delayed 212 on Thursday, according to data tracker FlightAware. Allegiant delayed 45% of its flights, and Sun Country delayed 23% of its flights. The companies did not provide details on how many flights were affected.
Microsoft said the outage began around 6 p.m. ET on Thursday, and that some customers were experiencing issues with multiple Azure services in the Central US region.
Azure is a cloud computing platform that provides services for building, deploying, and managing applications and services.
Microsoft said separately that it is investigating the issue affecting various Microsoft 365 apps and services.
