Mach number as posted in FA is very misleading. It is some bizzare interpretation of the groundspeed of the aircraft, and about the most useless and misleading thing I’ve ever seen on FlightAware.
In short, NO the 737 isn’t going mach 1. I’ll try to keep this simple.
“Mach”, or the speed of sound, varies depending on altitude. At sea level, the speed of sound, mach 1, is 761 mph. To figure out what mach 1 is at altitude, you multiply the constant, 761 mph, by a conversion factor, seen on the chart below.
**Altitude in feet Speed of Sound ratio **
Sea Level 1.00
5,000 ft 0.9827
10,000 ft 0.9650
15,000 ft 0.9470
20,000 ft 0.9287
25,000 ft 0.9100
30,000 ft 0.8909
35,000 ft 0.8714
40,000 ft 0.8671
50,000 ft 0.8671
60,000 ft 0.8671
Using the supplied aircraft track as an example, multiply 761 by the conversion for 39,000 ft, approx 0.868.
761x0.868= 660 mph
So, at 39,000 ft, mach 1 is approx 660 mph.
Now, the groundspeed of the aircraft in question reached or exceeded 660 mph. That is to say that the actual airspeed and a tailwind component acting on the aircraft added up to 660 mph. The actual airspeed of a 737 is typically .72 to .76 mach or therebouts.
In over 20 years or professional flying, I have never seen groundspeed expressed in mach, and have no idea why someone decided to do it on here.