It's a bit difficult to say, but my great grandfather was a WWI pilot, a flight engineer. He said that "flying was still in its infancy; planes were piano wire and canvas". He had a serious accident when the propeller hit his head when starting the engine, and still had the scar to show for it. A few days later another pilot died doing the same.
He witnessed several fatal crashes, and had a few emergency landing, and near misses; all this was while he was still in the UK. So I would say yes there were a lot of people killed accidently, in one way or another.