Controllers switched frequencies and planes were “safely separated,” officials said. The 90-second outage on Monday followed communications problems at Newark airport.

A portion of the Denver air route traffic control center experienced a 90-second loss of communications late Monday, the Federal Aviation Administration said in a statement.

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.