Drones are becoming more common and pose a risk to helicopter pilots. The Federal Aviation Administration requires all drones to fly within eyeshot of the individual controlling the remote. Drones must also stay out of airspace dedicated to helicopters and other manned aircraft.
Unfortunately, not all drone operators follow FAA regulations. A Robinson R22 helicopter turned on its side during an unbalanced landing caused by losing control after hitting a tree while trying to avoid a DJI Phantom quadcopter drone.