For the second time in just three days, a radar blackout at Newark Airport forced a ground stop on Sunday, plunging the busy hub into chaos and reigniting concerns about the nation’s aging air traffic control system.

The failure left air traffic controllers without radar or radio contact with aircraft, halting departures and arrivals and frustrating passengers already grappling with delays and cancellations. It was the third radar failure in two weeks at the Philadelphia-based facility responsible for Newark’s airspace.