The incident follows recent radar outages at New Jersey’s Newark Airport due to the FAA’s antiquated infrastructure, adding to safety concerns about flying in U.S. airspace.

US aviation safety regulators are investigating a communications outage affecting flights approaching Denver International Airport earlier this week, the latest in a series of glitches that have put a spotlight on the nation’s aging air traffic control system.

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.