I have a friend who did 6 months rotation as a trainee doctor in Guildford hospital's A&E dept. He has told me that about 20% of serious injuries (breaks and above) are equine related. There is an inherant risk involved by climbing on a horse. I do not discount that the accident in question is an awfully tragic - but scared pheasants startling horses have killed many more riders than low flying ac.
I'm not in any way anti-horse, my wife and I both ride, but I do find the horse community trying to ban low-flying as about as ridiulous as if we tried to ban power cables had we just flown into a set.... If either hadn't been there the accidents wouldn't have happened.
Just my 2p...for now.