Sounding a horn would only have people looking in the direction of the horn. It doesn't appear as though the pilot of this airplane did anything willfully reckless or problematic.. except not setting the failsafe to idle/kill on the engine, which would have at the very least reduced the energy of the crash by a great deal.

Sadly, I have flown at many airshows where people are allowed to fly who have much worse problems than this, only they've been lucky whereas this pilot wasn't. One pilot is repeatedly asked to fly at airshows, even though I've seen him routinely behind the safety deadline, and at least twice, was so far behind himself that he was actually over the assembled crowd and over the static display area. I have also heard of someone crashing a turbine so far behind the crowd line that it actually came down next to a hotdog vendor.

Just because you're able to takeoff and land at your local field does NOT mean you're capable or qualified to fly in airshows. We seriously need to do something in this country to get this under control in my opinion, or we're just another accident waiting to happen.