Jonathan Stewart was badly shaken by a recent close call in airspace around Newark, N.J. “I don’t want to be responsible for killing 400 people,” he said in an interview.

A veteran air-traffic controller at the facility that handles flights in and out of Newark Liberty International Airport is calling for more resources and speaking out about the intense pressures workers face amid a staffing shortage and tech outages.

As of May 7, all but two of the 313 air traffic control facilities in the United States were understaffed, a New York Times analysis found.