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

The outage at Denver International Airport happened Monday afternoon and affected communications, not radar, the FAA’s head of air traffic control, Frank McIntosh, said during a House hearing Thursday. This communications failure follows two high-profile outages of radar and communications in the past 2 1/2 weeks at a facility that directs planes in and out of the Newark, New Jersey, airport.

The FAA said in a statement that the Denver Air Route Traffic Control Center lost communications for approximately 90 seconds. McIntosh said both the primary and main backup frequencies went down, so the controllers had to turn to an emergency frequency to communicate.

“Controllers used another frequency to relay instructions to pilots. Aircraft remained safely separated and there were no impacts to operations,” the FAA said.

Rep. Robert Garcia of California told McIntosh during the hearing that “anytime there’s these outages which are happening now more regularly, it’s very concerning.”

“We know that there are staffing and equipment problems at air traffic control,” Garcia said. “We know that the problems have gone back decades in some cases, but it’s still an absolutely shocking system failure and we need immediate solutions.”

The Denver communications failure is the latest troubling equipment failure in the system that keeps planes safe. Last week, the Trump administration announced a multibillion-dollar plan to overhaul an air traffic control system that relies on antiquated equipment.

The Newark airport has generally led the nation in flight cancellations and delays ever since its first radar outage on April 28 that also lasted about 90 seconds. A second outage happened on May 9. In both those instances controllers lost both radar and communications.

The FAA was in the middle of a second day Thursday of meetings with the airlines that fly out of Newark about cutting flights because there aren’t enough controllers to handle all the flights on the schedule now. More than 100 flights have been canceled at Newark Thursday.

Officials developed the plan to upgrade the system after a deadly midair collision in January between a passenger jet and an Army helicopter killed 67 people in the skies over Washington, D.C. Several other crashes this year also put pressure on officials to act.