CNN —
Hundreds of U.S. flights were canceled early Monday as airlines scrambled to restore service, four days after a global technical outage caused massive delays and stranded travelers at airports across the country.
As of 7:30 a.m. ET on Monday, more than 700 flights to and from the United States had been canceled and more than 800 were delayed, according to flight tracking site FlightAware.
While most airlines have reduced the number of canceled flights, Delta Air Lines accounted for more than 600 of the flights canceled on Monday, according to FlightAware.
Delta Air Lines declined to comment on the figures, but in an update to customers Sunday afternoon, Delta CEO Ed Bastian said the airline was working to restore service after the outage.
The “biggest IT outage in history,” caused by a software update on Microsoft equipment late Thursday night and early Friday morning, took down computer and technology systems around the world, causing chaos at airports, halting 911 services and creating problems for medical facilities.
“In particular, one of our crew tracking related tools was affected and was unable to effectively process the unprecedented number of changes caused by the outage,” Bastian said in a statement.
The outage affected an estimated 8.5 million Windows devices — less than 1% of all Windows machines — according to a Microsoft blog post on Saturday, but the impact was widespread, affecting airlines, banks, businesses, schools, government agencies and even some medical and emergency services around the world.
Anderson Economic Group CEO Patrick Anderson told CNN that losses from the outages could exceed $1 billion, but it’s unclear if and how affected customers will be compensated.
Here’s what we know about the outage and its ongoing impacts.
The outage was linked to a software update rolled out by CrowdStrike, a major US cybersecurity firm whose software detects and blocks hacking threats and is used by many Fortune 500 companies, including major global banks, healthcare and energy companies, and the US government.
CrowdStrike told customers early Friday that the outage was caused by “a flaw found in a single content update for software on the Microsoft Windows operating system,” CEO George Kurtz said in a post on X. The issue was identified and isolated, and engineers have deployed an update that fixes the problem, Kurtz said.
According to the advisory seen by CNN, the company’s engineers have taken steps to address the issue and have instructed customers to restart their computers and take other measures if technical issues persist. The advisory said the issue is specific to CrowdStrike’s flagship software product, Falcon, and does not affect Mac or Linux operating systems. CrowdStrike said Falcon is designed to protect files stored in the cloud.
The company said the outage was not the result of a security incident or cyber attack.
Kurtz later apologised to customers, saying he was “deeply sorry for any inconvenience and trouble caused”.
In an update posted to LinkedIn late Sunday, CrowdStrike said a “significant number” of its 8.5 million devices were back online and running.
Confusion and confusion for travelers
More than 1,800 U.S. flights were canceled and more than 9,900 were delayed on Sunday, according to FlightAware. Major hotels, including Marriott International and some Hiltons, were affected by both delays in payment processing and check-in procedures.
U.S.-based carriers American Airlines, United Airlines, Delta Air Lines, Allegiant Air, Sun Country Airlines and Frontier Airlines all reported problems on Friday.
American Airlines said Friday morning that it had “safely resumed” service, while United Airlines said “most systems had been restored” by Friday night but warned the issues could still result in flight delays and cancellations.
Delta Air Lines suspended all flights on Friday morning because its systems were offline, and by Saturday, more than 3,500 flights on Delta and Delta Connection Airlines had been canceled, the airline said. The airline canceled 1,208 flights on Saturday and more than 1,200 on Sunday, according to FlightAware.
Delta Air Lines also announced that it would not allow unaccompanied minors to fly until July 24 because of the outage.
The department said Delta Air Lines is still experiencing large numbers of flight cancellations, and Transportation Secretary Pete Buttigieg met with the airline’s CEO, Ed Bastian, on Sunday afternoon.
“We continue to receive reports of unacceptable disruptions and customer service conditions at Delta, including hundreds of complaints filed with regulators. We have made clear our expectation that Delta will promptly provide refunds to consumers who do not wish to rebook, rebook free of charge for consumers affected by delays and cancellations, provide timely refunds for meals and hotel accommodations, and provide appropriate customer service assistance to all customers,” Buttigieg said in a statement.
Other airlines were also getting back on track over the weekend, including Turkish Airlines, one of the world’s largest carriers, which said on Saturday that “the global technical issue has been resolved. All our operations have returned to normal.”
On the same day, Jetstar Japan, Hong Kong Express and Cebu Pacific announced that operations were gradually recovering after disruptions caused by a global technology outage.
David Kennedy, co-founder of cybersecurity firm Binary Defense, told CNN on Saturday that even if the flawed computer update is reverted, it won’t be a quick fix for airlines, because they have computers at thousands of gates that would need to be rebooted individually.
“It’s not as simple as just restarting it. There are a lot of steps and complexities involved,” Kennedy said. “Airports and hubs just don’t have the manpower to do it.”
As travel disruptions continue, Buttigieg said in a social media post on Saturday that he’s received reports that some airlines are only offering flight credits to passengers on canceled flights.
“Let me be clear: if your flight is canceled and you don’t rebook, you are entitled to an immediate refund,” Buttigieg said.
Hospitals, 911 systems, and government agencies affected
Because CrowdStrike’s software was widely used, the outage rippled across numerous industries, including emergency communications, government services and healthcare.
Large hospital systems including Massachusetts General Hospital Brigham in Massachusetts, the University of Pennsylvania School of Medicine in Pennsylvania and the Mount Sinai Health System in New York all reported being affected by the outages on Friday.
Emory Healthcare in Atlanta said “surgeries at our outpatient surgery centers and hospitals will be postponed until the system stabilizes.”
Several cancer centers, including Dana-Farber Cancer Institute in Boston and Memorial Sloan Kettering Cancer Center in New York, have also suspended certain procedures and appointments.
Some blood banks have experienced disruptions as well.
And 911 service was briefly suspended in some areas, including Arizona and Alaska, but has since been restored.
Government agencies, including the Social Security Office and local Department of Motor Vehicles, also suspended operations due to the power outage.
Public transportation systems in Washington, DC and Pennsylvania were also affected by the outage but resumed service on Friday.
Mail delivery companies UPS and FedEx said they were continuing to operate but expected service delays on Friday.
