The National Transportation Safety Board (NTSB) on Tuesday issued two “urgent” safety recommendations after discovering thousands of close calls between helicopters and planes near Ronald Reagan Washington National Airport following a midair collision in January.

The National Transportation and Safety Board is recommending helicopters no longer fly along the route when planes are landing on specific runways at DCA.

Helicopters should be barred from a four-mile stretch over the Potomac River when flights are landing on Reagan National Airport’s Runway 33, National Transportation Safety Board Chair Jennifer Homendy said as the NTSB unveiled “urgent safety recommendations” after the deadly mid-air collision in January.