There is no indication of who broke the 400ft level: did the drone go over it or did the chopper go below it?<p>As for drone pilots keeping clear of aircraft, that is only possible when the aircraft are maintaining visual contact with all drone operators on the ground.<p>Ideally drone pilots would be able to receive smething similar to ADS-B signals and the ground control stations would all direct drones away from nearby aircraft. Sadly the resolution and accuracy of ADS-B in all four dimensions is insufficient to allow automatic avoidance of scenarios like the one posted.