At times Monday evening, as few as three air traffic controllers per hour were lined up to monitor via radar the planes flying into and out of the airport, the Federal Aviation Administration said.

The air traffic controllers directing planes into the Newark, New Jersey, airport lost their radar Friday morning for the second time in two weeks.

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.