Helicopters should not be allowed to travel over a four-mile stretch over the Potomac River following the deadly air collision near Washington in January, according to urgent safety

The National Safety Transportation Board has found that helicopter traffic out of Ronald Reagan International Airport posed an “intolerable risk to aviation safety by increasing the chances of a mid-air collision” ahead of a crash last month that resulted in the deaths of 67 people.

Federal investigators looking into the cause of the January collision between a passenger jet and an Army helicopter near Washington, D.C., that killed