This may have been covered in other thread(s), but after a quick search I didn’t see the answer. I use OnAir, and am currently flying the 320. OnAir states the 320’s cruise speed is 335K google says its economic cruise speed is 454K at FL 370. So why is it that in game at FL 370 or FL 380 i get overspeed warnings at 280K??
What you see as your airspeed on your PFD is your indicated airspeed (IAS).
Tthis depends on the speed of your aircraft relative to the air, but also on the density of the air. When the density goes down (e.g. because you’re climbing) so does your IAS, even if your speed relative to the air remains the same.
Your speed relative to the air is the true airspeed (TAS), and this is the speed that OnAir and Google are stating. You should also be able to see your TAS displayed in the ND.
For more reading: https://en.wikipedia.org/wiki/Airspeed
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Also be aware that there is a maximum Mach speed too. At speeds approaching ~.90 Mach, compressibility becomes a factor on conventional airfoils. Because the speed of sound gets slower in colder air, your Mach # at any given true airspeed will go up with altitude. Per Wiki, the cruise speed for the 787-10 is Mach 0.85, with 0.90 listed as max. When using autothrottle, you’re better off using Mach mode above FL180
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so I should just keep an eye on my TAs or GS speed then? Not IAS?
It depends. How your plane handles (e.g. when it will stall) mainly depends on IAS*. If you want to figure out how long it’s going to take you to get somewhere you want to look at your GS.
*For the pedantic / more precise people reading this, yes TAS and Mach number are also important, I’m trying to keep things simple.
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