A federal review of helicopter safety around some of the busiest U.S. airports has revealed dangerous flying conditions at the Las Vegas airport.

The Federal Aviation Administration said it has taken a number of steps to reduce the risk of collisions between helicopters and planes near Harry Reid International Airport in Las Vegas after an initial analysis uncovered “several immediate issues.

Three senior Democratic lawmakers on Tuesday urged the Federal Aviation Administration to address significant safety issues at Reagan Washington National Airport and maintain reduced air traffic after a series of troubling incidents.