An exclusive report by the New York Post claims that on Monday evening between 18:30 to 21:30, flights out of Newark Liberty International Airport (EWR) were handled by just one air traffic controller and a trainee. The report quotes a New York-based controller describing the situation as “pure insanity.” It also noted that an FAA spokesperson said that there were at least three controllers scheduled for each hour on Monday night but did not clarify how many of them were fully certified personnel.
The New York Times reported something similar, adding that four people familiar with the situation said that the number of fully certified controllers on duty to manage Newark’s air traffic was sometimes one or two. These figures are shocking because the target number of controllers for Newark to manage traffic in those hours is around 14-15.
https://en.wikipedia.org/wiki/2002_Überlingen_mid-air_collision
One of them followed TCAS, according to procedure, the other one mistankenly thought they were supposed to follow ATC. So they both ended up going the same direction.
New Standard Operating Procedure that is clarified after the accident is that you always ignore ATC and follow the TCAS Resolution Advisory.
If ATC says anything, pilots are supposed to say “Unable, Resolution Advisory”