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.
The Big 12 Conference said Friday it is "evaluating any potential changes to Saturday's football schedule" due to the national ground stop.
"The Conference will continue to monitor the travel disruptions alongside its member institutions and provide updates for Saturday's games," the college athletic conference said in a statement.
A small number of flights are taking off over the ocean and in Alaska and Hawaii.
Alaska and Hawaiian Airlines said in a statement that flights within Hawaii and from the West Coast to Hawaii can continue. International flights from Hawaii are also cleared.Â
Hawaii's Department of Transportation said that flights between Anchorage to Oakland and Hawaii can fly.
San Francisco International Airport said that Pacific-bound flights are cleared to depart from the airport, including to destinations in Alaska and Hawaii.
Ontario Airport in California said that flights heading west over the ocean are allowed to take off from the airport at this time.Â
Boston Logan said in a post that the FAA is permitting some transatlantic flights to depart.
-ABC News' Bonnie McClean
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
