avoid flying towards people. >> there hasn't been a spectator fatality since 1952 that's because of the strict rules. >> reporter: there are new rules when it comes to the world of air races after this crash last september. a p-51 mustang slams into the crowd in reno, nevada. 11 people were killed. federal investigators found the plane had performance modifications that were undocumented and untested. stricter rules, more training for pilots, and changes to the race course to better avoid spectator. >> you will see people flying to the edge of the envelope and that means assumed risk for any audience member. >> reporter: for many a thrill worth taking. clayton sandel, denver. >> scary footage.