Boom Supersonic’s XB-1 demonstrator plane just went supersonic in the skies over California’s Mojave desert, making it the first civil aircraft to break the sound barrier. The American startup’s plane notched the historic achievement in its twelfth test flight. It cleared Mach 1 and stayed supersonic for around four minutes, reaching Mach 1.1. Test pilot Tristan Brandenburg broke the sound barrier two more times before receiving the call to bring the XB-1 back to the Mojave Air & Space Port. The...