This story was updated at 2:00 p.m. Eastern.

At 6 a.m. Eastern Time on Friday, 512 flights in the U.S. had been canceled due to a global outage impacting computers running the Microsoft Windows operating system. By 2 p.m., the number of nixed flights had more than quadrupled to 2,335, according to data from FlightAware. That number will surely climb higher throughout the morning.

The FAA is “closely monitoring a technical issue impacting IT systems at U.S. airlines. Several airlines have requested FAA assistance with ground stops for their fleets until the issue is resolved,” the agency told Forbes in an email.

Up to 3.7 million passengers are flying out of U.S. airports on Friday, according to Cirium, an aviation analytics company, on roughly 24,000 scheduled domestic flights and 3,000 international flights.

To put things in perspective, holiday travel on December 23, 2022, was disrupted with some 5,300 flights canceled in the US, or about 23% of flights. “Today will be close to that amount,” says a Cirium spokesperson, noting “37% of flights have departed today with a 30-minute delay or greater in the U.S.”

At noon Eastern, the five U.S. airports with the most cancellations were Atlanta’s Hartsfield-Jackson (283), Chicago O’Hare (108), Minneapolis/St Paul (90), New York’s LaGuardia (85), and Newark (83).

At that time, Delta Air Lines reported the most cancellations in the U.S., with 777 flights; United Airlines and American Airlines and have tallied 367 and 362 canceled flights, respectively.

_{Flying on Friday? Use These Tips}

Put your airline in your pocket. At the very least, you should download your airline’s app, which will let you monitor your flight’s status and sign up for text notifications. But the real superpower of an airline app reveals itself in the event of a delay or cancellation, since it can be a fast path to rebooking another flight. This is a situation when quick action definitely matters.

Most passengers will mob the airline help desks at the airport to get rescheduled, but it’s almost always faster to rebook through the app, at an in-airport kiosk or by calling the airline’s toll-free number, which you should program into your smartphone’s speed dial before you get to the airport. If you have elite status with your airline’s loyalty program, you may find shorter lines at the help desk in the club lounge.

Track your flight. The FlightFinder tool on FlightAware can give travelers an early heads-up that a problem may be brewing—often even before your airline alerts you. Enter your flight information, and then click the “Where is my plane now?” link just under the flight number. You’ll be able to see if the plane is ahead of schedule, on time or behind schedule and you can act accordingly — even before the airline announces a delay or cancellation.

Grab a nicer seat. If you find yourself facing a long delay or cancellation, LoungeBuddy can make an unexpected layover much more bearable. Virtually every large airport now features multiple airport lounges that offer day passes, which is good news for travelers who don’t have access to lounges through elite airline status or a credit card benefit.

LoungeBuddy sells day passes to over 400 airport lounges in 68 countries around the world, typically for between $25 and $60. You may also be able to buy your way into branded lounges such as American Airlines Admirals Club, Alaska Lounge, Delta Sky Club, United Club, American Express Centurion Lounge and more.

Tap your credit card app. Depending on which credit card you use to book your flights, you may have built-in travel insurance — including trip delay or trip cancellation coverage — to help with any extra expenses you end up incurring. Downloading your credit card provider’s app will put this helpful information at your fingertips when you travel.

Ask for help. If you’re not up to speed on flyer’s rights, AirHelp can help you figure out if you’re eligible to receive compensation for a delay or cancellation. You’d be out of luck if your flight was canceled or delayed because of a weather-related event, but it’s less certain if you will be owed something when the disruption is caused by a technical issue.

“It’s crucial for passengers to understand their rights and know their options during disruptions, says AirHelp CEO Tomasz Pawliszyn. “Although this incident is beyond the control of airlines and airports, passengers still have certain rights under U.S. Department of Transportation (DOT) regulations. The passengers are entitled to assistance from the airline. This can include rebooking on the next available flight and, in some cases, meal vouchers and accommodation if the delay extends overnight.”

Pawliszyn’s advice: “Passengers should retain all boarding passes and receipts for any expenses incurred during the delay, such as food, drink, and accommodation, to facilitate any potential reimbursement claims.”