answer:Apparently, as slow as zero mph. The Concorde was supersonic (2.2 mach), and compared to today’s jumbo jet liners, was relatively small. Of course, it’s no longer flying. Gulfstream makes several planes, the largest of which can carry up to 18 passengers at speeds approaching 0.90 mach. Virgin Galactic’s Spaceship Two -class sub-orbital craft reach speeds of 3.0 mach.