Air traffic controllers in Denver lost communications with planes 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 a control facility that directs planes around Denver International Airport on Monday afternoon 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 in Philadelphia 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 these outages are happening more regularly and it’s concerning every time.

“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.”

Last week, the Trump administration announced a multibillion-dollar plan to overhaul an air traffic control system that relies on antiquated equipment. Air travel is safe even if the air traffic control system is old, but the problems in Newark were unacceptable and could have been prevented if the system had been upgraded sooner, said Transportation Secretary Sean Duffy in a Thursday op-ed in Newsweek.

The Newark airport has generally led the nation in flight cancellations and delays ever since both radar and communications went out on April 28 and again on May 9. A third similar problem happened Sunday, but that time the backup system worked and kept radar online.

“The safety of the traveling public cannot continue being put at risk,” Democrat and ranking member Rep. Rick Larsen said after the hearing. “Problems with our system have crossed administrations, but safety improvements cannot span generations. We need action now.”

The FAA and airlines that fly out of Newark met again Thursday to discuss cutting flights because there aren’t enough controllers to handle them all. More than 140 flights have been canceled at Newark Thursday.

Officials developed the plan to upgrade the air traffic control 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.