The Federal Aviation Administration (FAA) ordered a nationwide ground stop on Friday, moments before Shabbos, halting departing flights at airports across the United States, including Newark Liberty International Airport and other New Jersey-area airports.

The FAA said the ground stop was issued following communications issues impacting multiple Air Route Traffic Control Centers. The agency said technicians were investigating the problem, which affected communications and radar systems used by air traffic controllers.

Transportation Secretary Sean Duffy said the problem began at approximately 3:36 p.m., when air traffic control centers and radar systems across the country began experiencing instability. Officials said the systems were providing inconsistent information, prompting the FAA to ground flights out of an abundance of caution.

At the time the order was issued, more than 3,500 aircraft were in the air. Officials said air traffic controllers and pilots safely brought the aircraft down using established safety procedures.

During a briefing, Duffy said the incident exposed problems with the country’s aging air traffic control infrastructure, explaining that older communications equipment and overloaded routers contributed to the outage. A contractor had been working to replace older copper wiring with fiber-optic lines when the problem occurred.

The nationwide ground stop was lifted at approximately 8:15 p.m. Friday after the FAA tested its systems and confirmed they were stable. However, thousands of flights were delayed or canceled, with disruptions continuing into Saturday.

Homeland Security Secretary Markwayne Mullin said officials found no indication of a cyberattack or other malicious activity, reassuring the public that there was no reason to believe the incident was the result of an intentional attack.

FAA Administrator Bryan Bedford said Saturday that officials believe the worst of the disruptions is behind them, although passengers should continue to expect delays and cancellations as airlines work to restore normal operations.

Federal officials said they are continuing to investigate the incident and address the vulnerabilities in the nation’s air traffic control system.