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.

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

“I equate a good, A-level, traffic controller that can handle a place like Newark, JFK, LAX, San Francisco, to a three dimensional chess player who can juggle a chainsaw, an axe, a sword, a razor blade with his eyes closed,” Aero Consulting Experts CEO and a former United pilot Ross Aimer told Fortune.

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.