Mach number

At altitude, for reasons explained, Mach number is a function of temperature.

More specifically, it is a flow whose Mach number exceeds 1.

A sign inside the cabin displays the Mach number continuously.

Or sound would, at that Mach numbers corresponding to those speeds, if it could?

The above equation is only for Mach numbers less than 1.0.

Mach number is given as a percentage compared to the local speed of sound.

The new intake also was designed to be more efficient at higher Mach numbers.

Mach numbers up to 4 are easily obtained without any additional heating of the flow.

With heating, Mach numbers of up to 11 can be reached.

So, the Mach number is a multiple of the speed of sound.