The FAA issued the order shortly after 2 p.m. MT, citing "extraordinary circumstances." Aircraft already in the air were permitted to land, but departures were frozen at Denver International Airport and airports across the country.

By 6:30 p.m., DIA had recorded 640 delays and 369 cancellations, according to FlightAware. Airport officials said before 6 p.m. that they could accommodate all incoming flights, that every gate was in use, and that some passengers were being deplaned on the tarmac.

At a White House press conference, Homeland Security Secretary Markwayne Mullin said the disruption stemmed from a telecommunications outage and that there was no indication of a threat to the United States.

"Right now things seem to be working, as you can see, in the right direction," Mullin said. "The public was never at danger in this process. We did it out of an abundance of caution."

Transportation Secretary Sean Duffy said air traffic control servers returned inconsistent data, causing the outage, and attributed the failure to old hardware. He urged Congress to fund deployment of a new system. Mullin said the overloaded servers did not appear to have been caused by a cyberattack, and that President Donald Trump had declared the problem a national emergency, though it was not clear Friday night whether a formal declaration had been issued.

Mullin could not confirm whether the ground stop was connected to the national rollout in recent days of a new AI-powered air traffic tool.

As the shutdown stretched into the evening, Denver city spokesman Jon Ewing said DIA would set up cots and distribute blankets to stranded passengers. Concessions would remain open, particularly so families could buy formula and diapers, and travelers needing extra help were directed to the information desk. Airport officials said the information center would stay open until 2 a.m. and that therapy dogs would be on hand.

The Westin hotel at the airport was fully booked for the night.

Passengers described a scene that was calm but disruptive. Susan Rinkunas, traveling from Boulder back to New York, said the mood at DIA was subdued.

"Either people don't really know this is happening or they're just resigned to delays because it seems kind of normal in this airport right now," she said. Rinkunas later rebooked for Saturday and planned to share a hotel room with a colleague.

Jason and Brittney Stoffel learned their 3:45 p.m. flight had been canceled only minutes before boarding. Their trip to visit Brittney's mother in Albuquerque was pushed to 8 a.m. Saturday, and an Uber back to the Westminster area cost $140.

"We heard nothing about delays. We're literally walking up to the gate, about to board, 10 minutes before takeoff, and then we get a text that everything was canceled," Jason Stoffel said.

Passengers leaving the airport also faced long waits to reclaim checked bags, with some told it could take hours. Travelers trying to return to Denver were stranded as well. Nell London, a journalist who works with Colorado Public Radio's Colorado Matters, was stuck at the airport in New Haven, Connecticut.

"Every seat is taken, lots of people are sitting on the floor," London said. "But everyone's fairly calm and in good spirits so far."

The effects rippled through smaller airports around the state. Colorado Springs Airport spokesperson Aidan Ryan said its runways can handle any size aircraft and that it was prepared to accept diverted flights. At Grand Junction Regional Airport, four airlines rescheduled flights Friday afternoon, according to Ben Peck, the airport's director of facilities, who said the FAA had promised further updates.

"We're just trying to share whatever information we get from the FAA when they release information," Peck said. "The majority of the handling of the incident is the airlines with the passengers directly."

At Aspen/Pitkin County Airport, the disruption hit during the off-season, when carriers operate a reduced schedule, said communications specialist Kelsey Petersen. Private and commercial aviation were both affected, she said, but the airport is accustomed to working around disruptions.

"Operating at the Aspen/Pitkin County Airport, we are subject to weather cancellations or weather delays often and weather impacts us a good bit," Petersen said. "So we roll with the punches here."

The National Weather Service reported nationwide internet and communications outages and its website went down, though it was unclear whether those problems were related to the FAA's outage. The weather service office in Boulder said it experienced no internet or communication issues.

The last nationwide ground stop occurred in January 2023 because of a communications system failure; before that, the most recent was on Sept. 11, 2001. Significant delays of this kind can cascade for days as airlines work to reposition aircraft and crews.