I had a professor that was a single-engine light-aircraft pilot. He explained this phenomenon in one of our classes, and he theorized that JFK Jr's crash had the graveyard spiral as the main cause. It was at night, he had an injury to his ankle, and it was a plane that he wasn't that experienced in. No mechanical failure, no distress call, and death on impact means that it was likely that he didn't know that he was going down until just before impact.