The outage, which the Department of Homeland Security described as a telecommunications failure affecting regional air traffic control centers, disrupted travel across the country and left lawmakers and passengers demanding to know how a single point of failure could bring the system to a standstill.

Rep. Ted Lieu, D-Calif., called the FAA telecommunications outage "completely unacceptable" and said the agency must build systems that cannot be taken down by one failure.

"I urge the FAA and the Trump administration to make sure this never happens again," Lieu said in an interview Friday. He called for congressional hearings into the cause of the technical problem and the improvements needed to prevent a repeat.

"What just happened is enormously damaging to trust in our air system," he said, "and our air system is a vital component of our national economy."

Sen. Tammy Duckworth of Illinois, the ranking Democrat on the Aviation, Space and Innovation Subcommittee, said she would demand answers from the FAA.

"The safety of our skies is built on redundancies," Duckworth said in a statement. "Whatever led to the nationwide ground stop will warrant a thorough and complete investigation."

Rep. Ro Khanna, D-Calif., who was stranded at Denver International Airport because of the outage, told CNN that lawmakers were waiting to be briefed by the administration Friday afternoon.

At the White House, Homeland Security Secretary Markwayne Mullin said the ground stop did not constitute a national security threat.

"There is no indication that we've had, no reason to believe, that as of right now this was a threat to the United States," Mullin told reporters, later adding there was "no indication as of yet that this was a nefarious attack against us."

Federal officials have not identified a cause and are not ruling out a possible connection to a newly expanded artificial intelligence tool used to help manage air traffic. The FAA said Tuesday that it had expanded the tool, called Strategic Management of Airspace, Routes and Trajectories, or SMART, to all 22 of its control centers. According to an agency fact sheet, SMART combines roughly 200 data streams — including flight paths, schedules and weather — into a single cloud-based system.

Democrats raised concerns after the platform's initial rollout in the Washington area, calling in an October letter to Transportation Secretary Sean Duffy for a 90-day pause until lawmakers better understood how it is being used. They cited an "egregious lack of transparency" about the tool.

"The air traffic control systems and processes currently in place are complex, and we don't know what impact AI-enabled tools might have on these systems and resulting safety," the lawmakers wrote.

Air Space Intelligence, the company that created SMART, said in a social media post Friday afternoon that "current ground stop is not based on or a result of the SMART system, any product of ASI or our integration with FAA and ATC."

The episode has thrust the condition of the nation's air traffic infrastructure into the center of a growing political fight, with Democrats arguing that years of underinvestment and a rush to deploy new technology without adequate oversight have left travelers exposed. For communities that depend on reliable air service, the shutdown underscored how quickly a technical failure in one part of the system can ripple across the country.

Lieu said the damage goes beyond a single day of delays. "What just happened is enormously damaging to trust in our air system," he said, adding that the system is "a vital component of our national economy."