Millions of U.S. travelers were left in limbo on Friday afternoon after the Federal Aviation Administration announced a nationwide ground stop covering all U.S. airports. A ground stop is one of the FAA's most sweeping traffic-management tools — it halts departures across the affected airspace while flights already airborne generally continue to their destinations — so an order covering every U.S. airport brought departures to a standstill across the country. Hours later, the order was lifted, and federal officials used the disruption to renew calls for funding to modernize the country's aging air-traffic infrastructure.

Transportation Secretary Sean Duffy initially attributed the outage to a communication issue affecting all Air Route Traffic Control Centers. At a White House press briefing on Friday night, Homeland Security Secretary Markwayne Mullin said the disruptions stemmed from technology upgrades that were "overwhelming" the antiquated equipment. "It's going to continue to fail," he warned.

Mullin also addressed speculation about foul play. Despite recent hacking incidents involving freezers in Europe and at U.S. military bases, he said it "doesn't appear" that a cyberattack was involved, though he conceded that "there's nothing certain right now." Earlier in the day, he had ruled out terrorism, saying "This isn't another 9/11." With officials themselves flagging the uncertainty, the immediate question for travelers and airlines is whether that preliminary assessment holds as the agency works toward a definitive account of what failed.

Notably, the ground stop came just days after the FAA announced it would deploy an AI tool to help air-traffic controllers.

During the briefing, Duffy likewise suggested the problem involved old equipment being overloaded. "Our fix gives us a pretty good indication that it was a legacy network problem that went down," he said. He called on Congress to provide emergency funding to fix the FAA's aging systems, saying the Trump administration needs another $30 billion, before putting the total price tag at $50 billion.

The massive disruption came the same week that airlines in Europe suffered a wave of phony bomb threats. While all of the threats appeared to be hoaxes, at least one flight was diverted to a military base in France. Spanish Foreign Minister Jose Manuel Albares said Friday that Europe appeared to be facing "hybrid aggression and a form of psychological warfare."

Meanwhile, consumers are still grappling with the aftermath of a Microsoft outage that shut down email, collaboration, and AI functions. The company said Friday it had no indication that the ground stop was related to its global outage. The National Weather Service also said its radar systems saw no disruption on Friday, denying online talk that it had caused the FAA's communications issue.

Friday's incident was not the first nationwide ground stop in recent memory. The FAA last issued one in 2023, when files related to an alert system for pilots were unintentionally deleted, delaying thousands of flights before service resumed soon after the disruption. Earlier this year, flights at New York airports were halted when a contractor accidentally cut a fiber communications line in New Jersey. That string of infrastructure failures — some accidental, some deliberate — is now the backdrop for Duffy's funding request, and how Congress responds will help shape how quickly the FAA can replace the legacy systems its own officials warn keep failing.

This story was originally featured on Fortune.com.