Having sat in choppers at Avalon Airshow many times doing the sightseeing joyflights, I've always been impressed with the tight control over the departing and arriving flight paths, which basically never cross. Both arriving and departing choppers, including other traffic, depart towards the south and arrive in the same direction. Admittedly they have the advantage of a dedicated ATC team at the apron but the traffic pattern rules ensure that a similar collision to this one is almost impossible to imagine.