Caught in the middle of the issues at Newark is United Airlines, which is the most active airline at the New Jersey airport. While the problems lie with the FAA system, the airline is where people often aim their frustrations over cancellations and delays.

Operations are returning to normal after a runway equipment issues prompted ground stops at Newark Liberty and Hartsfield-Jackson Atlanta International airports Sunday, the Federal Aviation Administration announced.

Several times over the last year, Newark controllers lost radar or radio service, leaving them unable to talk with planes they were tracking.

The latest incident highlights the air-traffic-control network's aging infrastructure and comes a day after Transportation Secretary Sean Duffy proposed spending billions of dollars to fix it over the next three to four years.

United Airlines Holdings Inc. expects flight reductions at Newark airport to linger through summer and into fall as the crucial travel hub struggles to recover from air traffic control glitches that have already disrupted hundreds of flights.

Transportation Secretary Sean Duffy provided an update on Newark Liberty International Airport Monday afternoon. The Federal Aviation Administration briefly slowed air traffic at the airport Sunday because a new telecommunications issue affected the Philadelphia facility that guides planes into and out of New Jersey’s largest airport.