I was watching a test flight on flightradar24.com a few days ago. The test aircraft was at 40000ft at 565 kts. Very impressive indeed for it to be at about m0.9 its usually gulfstream territory. please correct me on my mach calculation if im wrong.

steve

Was the listed speed true or ground speed. If 565 was the ground speed than the actual true or mach would be different depending on the wind component at FL400.