The DHS secretary said there were no indications of a cyberattack.
The Federal Aviation Administration ordered a rare nationwide ground stop for all airports Friday -- a more than four-hour disruption that snarled travel from coast to coast with canceled flights and stranded passengers.
At a White House news conference Friday night, Transportation Secretary Sean Duffy blamed old technology that became overloaded and called on Congress to provide billions more in funding to modernize critical equipment, calling the situation an "emergency."
Department of Homeland Security Secretary Markwayne Mullin told reporters there was no indication the incident stemmed from a cyberattack, but that officials were still investigating.
Thousands of flights were canceled amid the ground stop.
"I believe that it's going to take us some time to get back to capacity," Duffy said when asked how long air travelers should expect delays and cancellations to continue.
Transportation Secretary Sean Duffy said in an X post Friday that the ground stop was "due a communication issue impacting all Air Route Traffic Control Centers."
Air Route Traffic Control Centers are responsible for communication for all flights above 18,000 feet. There are 22 of these towers located in some of the nation's major hubs including New York, Los Angeles and Atlanta.
In an update shortly after 6 p.m. ET, the FAA said that the ground stop remains in effect.
"As enroute facilities recover, flights will be allowed to depart through coordination with the air traffic control system command center."
-ABC News Ayesha Ali
Major airlines are offering travel advisories and waivers.
Delta has issued a waiver allowing passengers to change their flight at no extra cost for Friday and Saturday.
United has issued a travel alert, and told passengers, "You can reschedule your trip and we’ll waive change fees and fare differences."
"But, your new flight must be a United flight departing between November 12, 2026 and November 20, 2026. Tickets must be in the same cabin and between the same cities as originally booked," United added.
-ABC News Clara McMichael
AirSpace Intel, the contractor behind the SMART AI system that has been rolling out at facilities nationwide, put out a statement on X about the ground stop.
"The 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 company said.
-ABC News' Ayesha Ali and Clara McMichael
