Mach 1.01 GLEX (HBJER) … G/tracklog

scroll to 8:39pm
look at the speed in the 4th colum (610kts)

Isn’t that a bit too fast for a GLEX?

Radar displays ground speed not true or calibrated airspeed.

An extreme example – if you’re going 100kts and have a 700kt tail wind, you’re only moving through the air at 100kts even though you’re moving across the ground at 800kts, and thus are far below the speed of sound.

FWIW, 610kts @ FL410 is about M1.06 on a standard day.