They can also seriously damage low-flying fixed-wing tankers, which is why tankers must leave the area immediately if a drone is sighted.

There is only one known instance of a drone / helicopter collision. The drone exploded and the helicopter got scratches. Still dangerous though, don't do it.

Just as with a bird strike, a drone can cause harm to any low flying firefighting aircraft. Sighting any drone in the airspace of a wildfire causes all air operations to be suspended until it is gone.