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.
Homeland Security Secretary Markwayne Mullin reiterated that there was "no cyberattack" at the top of a press briefing Friday on the ground stop.
"I just want to reiterate this: The public was never at danger through this process. There was never any lives at risk. There was no flights at risk," he said.
The FAA said the nationwide ground stop is over, after more than four hours.
Transportation Secretary Sean Duffy and Homeland Security Secretary Markwayne Mullin will address reporters in the White House Briefing Room shortly regarding the FAA ground stop.
Amid the ground stop, United Airlines said it plans to cancel the majority of its remaining flights for the night, with exceptions for some international flights.
JetBlue said it is also canceling all remaining flights on Friday, save for Europe-bound flights departing from JFK and Boston.
"Flights already in the air are continuing to their destinations," JetBlue said in a statement. "We expect disruptions to continue into tomorrow, including additional cancellations."
Air Canada said it has canceled all remaining flights Friday between Canada and the U.S. due to the ground stop.
