IAS TAS and Ground Speed
(Virtual/PC pilot)
I've noticed that as you ascend to your cruise altitude of 360, your 'speed' drops in the primary display. Additionally, I notice that max speed (Vne?) reduces as well. My reading leads me to believe that the speed reduction on the primary display reduces because the air pressure on the pitot decreases, or less air is being forced in. But why does the Vne reduce as you climb? Is it a calculation of Vne based on altitude?
Then I see we have Ground Speed. So that would be using GPS over the ground, I'm guessing. Is that what ATC would see, when the aircraft reports speed?
Then we have IAS... So indicated airspeed would match what we see on the primary display, I think.
And TAS would be the real speed the aircraft is moving through the air, regardless of pitch (i.e. If we were climbing vertically, speed would not be 0 - it would be relative to the airflow).
Is TAS based on the altitude (air pressure).
If all of these are correct - why wouldn't the primary display just display TAS, which seems to be the most important speed for the pilot? With Ground Speed being the most important to ATC. IAS seems to be the least useful.