US authorities have not ruled out a full restoration of air traffic after the disruption by the end of the day.
The airports are gradually returning to normal operations.
The head of the Federal Aviation Administration, Brian Bedford, said that now "the worst is behind us", reports the Associated Press. Transport Minister Sean Duffy said there was a communication breakdown during the contractor's work.
"When replacing old copper cables with optical fibers, the system was overloaded, which led to communication interruptions and outages in the radar coverage areas," explained the head of the department.