[fedupjohn]

According to this link, Mach 1 at 41,000 feet is 660 mph. So, M89 would be 587 mph. According to FlightAware at 9:38 am, Flight 1146 was doing 655 mph at 41,000.

But they were flying West to East so they had a tail wind. Flightaware's listed speed is ground speed not air speed.

I once flew a 747 to Amsterdam at 755 MPH ground and asked the flight attendant if the pilot knew we were 'Flying Mach +'. She looked up at the flight chart and went and asked the pilot.

She returned with the answer, "according to the pilot we have a 170 mph tail wind which is added to the air speed to get your ground speed".

[cynwoody]

Flightaware's listed speed is ground speed not air speed.

Ah. That makes sense.