This is a specially modified P51 with a shortened fuselage in order to race at these speeds. The original P51's were capable of speeds of 600mph when in a dive and this is why we won the war. But something went wrong with this plane and it sounds like it was the horizontal trim which MTgas stated. The G's would have been tremenous for a young pilot but this guy was 72 I believe. I did hear that he made a mayday call though. If so, I assume it was b4 he passed out.