At times Monday evening, as few as three air traffic controllers per hour were lined up to monitor via radar the planes flying into and out of the airport, the Federal Aviation Administration said.

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

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.

The Federal Aviation Administration recently announced a three-year plan to upgrade air traffic control systems nationwide.

“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.

A reporter asked Duffy on Monday why the first Trump administration chose not to address the air traffic control system during his first term in office, noting that Duffy said it was a “decades-old” problem. However, Duffy’s answer left many users on social media scratching their heads.

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.

The United States aviation industry continues to grapple with the worst air traffic controller shortage in nearly 30 years as a recent spate of incidents has thrust the high-stress profession into the spotlight.