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.

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.

Air traffic controllers in Denver lost communications with planes for 90 seconds earlier this week and had to scramble to use backup frequencies in the latest Federal Aviation Administration equipment failure.