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.

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.