Hi Robin747-400 and has a cruise speed of
460kts I can only get 241kts at FL410.
What does the Mach number represent and how does it work in
regards to flying? The above mentioned 747-400 has a mach value of 0.9 which
means nothing to me.
The Mach is the speed of sound ie mach 1 is about 600kts however at altitude
your airspeed indicator becomes a little inacurate due to the very thin air. at
sea level this is at average 1013hpa droping 2hpa every 1000ft so at 40000ft
you have a air pressure of 933hpa. So it shows about half of true airspeed at
The 747 400 has a crise of M0.84 and a max altitude of 45100ft.
when you are climbing say at 310kts watch the Mach value (this should be the
little window on the asi) when it reaches M0.76 select that speed and continue
to climb and at the cruise you may select M0.84 and continue with that.
when decending when your desiged airspeed ie 290kts then select back to
ias(indicated air speed)
hope this helps