The air traffic system meltdown at Newark Liberty International Airport last week “was the most dangerous situation you could have,” according to an air traffic controller on duty that day, as the fallout from the outage stretches into a second week.

Air traffic controllers have been under strain for years, but a 90-second equipment failure last week exposed how decades of staffing shortages, underinvestment and patchwork solutions for those who guide planes through some of the world’s most congested airspace are taking their toll.