The incident follows recent radar outages at New Jersey’s Newark Airport due to the FAA’s antiquated infrastructure, adding to safety concerns about flying in U.S. airspace.

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.

Denver airport’s air traffic control was reportedly struck by a staggering six-minute outage earlier this week after several radio transmitters suddenly went dark. The frequency outage meant that as many as 20 pilots were unable to reach air traffic controllers as they descended into Denver International Airport on Monday afternoon,

On Wednesday, Newark led the nation with 42 canceled departures and 46 canceled arrivals, according to FlightAware.com. That’s even after United cut 35 daily flights at the airport starting last weekend.

Air traffic control towers are under-staffed and under-funded. Here's why that's been so difficult for Washington to solve.

Similar to last summer, there is currently a nationwide shortage of air traffic controllers, which will “take time” to replenish, according to Transportation Secretary Sean Duffy.

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.