EDMONTON — No one will ever know what caused the fatal crash of a private single-engine vintage plane in front of horrified spectators at an air show in Alberta. The Transportation Safety Board of Canada says. ground level, within. The first signs of trouble on Air Canada 797, a DC-9 flying at 33,000 ft. aircraft lavatories be equipped with smoke detectors and automatic fire extinguishers. Within five years, all jetliners…