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.

The FAA's Enhanced Air Traffic-Collegiate Training Initiative Program trains students with basic control and aviation administration skills.

“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.

Duffy laid out an extensive plan to replace the nation’s outdated air traffic control system last week, including installing 4,600 new high-speed data connections and replacing 618 radars, but didn’t put a price tag on the plan other than to say it will cost billions.

One air traffic controller (ATC) and a trainee will operate every flight in and out of Newark between 6.30pm-9.30pm — despite 15 staffers being the standard requirement for a shift.