The air traffic control mishap early Friday morning added to disruptions in recent days that have intensified concerns about safety at one of the busiest U.S. airports.

Operations have returned to normal after another air traffic control equipment outage caused the Federal Aviation Administration to implement a ground stop for Newark Liberty International Airport-bound flights Sunday morning.

There was a telecommunications outage that impacted communications and radar display at Philadelphia TRACON Area C, which guides aircraft in and out of Newark Liberty International Airport airspace. The outage occurred around 3:55 a.m. on Friday, May 9, and lasted approximately 90 seconds.