Frontier and other airlines were at a standstill for hours after a massive Microsoft outage

A significant Microsoft outage brought low-cost carrier Frontier Airlines and some competitors to a standstill for hours after a regulator halted departures. The ground stop was lifted late Wednesday night.

“Our systems are currently impacted by a Microsoft outage, which is also affecting other companies,” Frontier said in a statement on its website. “We appreciate your patience.” The company was offering refunds to inconvenienced passengers.

The Federal Aviation Administration said Frontier asked it to pause the airline’s departures across the United States. A little after 10 pm ET, the FAA lifted the ground stop on Frontier.

The airline has cancelled 131 flights Thursday and delayed 223 others, making up nearly 30% of its overall flights, according to data tracker FlightAware.

Allegiant and SunCountry also said on their websites that they were having difficulties.

“Due to a global outage at a third party vendor, our booking, check-in, and trip-managing capabilities are temporarily unavailable,” SunCountry said on its site.

“The Allegiant website is currently unavailable due to the Microsoft Azure issue,” Allegiant said.

Microsoft on its Azure cloud software status report site, said that around 6 pm ET, the service went down for some customers in the Central US region – “including failures with service management operations and connectivity or availability of services.” The company said it determined the cause and is working to fix it. A company spokesman did not immediately respond to a request for comment.

Other airlines were unaffected by the outage. United, Southwest and American Airlines said they were not impacted by the outage.