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Altitude


Donald Stimson
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I am running the newest version 3.3.1 with MSFS and Prosim A320. Currently I am on FL300, altimeters on STD with a current QNH in the area of 1014. On ForeFlight, it shows my aircraft at 30038ft, looking quite right. But on Vatscope, SimAware etc. I am at FL310. How can this be?

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19 hours ago, Ross Carlson said:

VATScope, SimAware, etc. show your true altitude, not your pressure altitude. I'm guessing that foreflight is showing your pressure altitude when you're in the flight levels. (As it should.)

Even if I turn on temperature correction in the aircraft settings, it only changes a couple of feet, but I am never coming close to what Vatsim sees, which it should, if it was really true altitude at 1014 QNH. In the current flight it is even worse: Vatsim shows FL380 although FL360 is indicated. If I turn in local pressure or temperature compensation, I only get around 200ft less, but nowhere near to close the 2,000 ft gap. Something is off here.

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I'm confused as to what the actual problem is. When you say "VATSIM shows FL380" what do you mean? There are many places in "VATSIM" that you could be referring to.

My point in my previous reply is that you cannot compare what you see in VATScope and SimAware with what you see in ForeFlight, as they may not be reading the same values from the sim.

Developer: vPilot, VRC, vSTARS, vERAM, VAT-Spy

Senior Controller, Boston Virtual ARTCC

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I mean by that that the altitude seen on Vatsim apps like Vatscope is far off from what I have indicated or is broadcasted to apps like Foreflight. And on top of this, ATC then, probably because they see what I see an Vatscope, SimAware etc., keeps asking me why I am several FLs off from what I told them or what my cruising alt should be according to my filed flightplan.

My actual problem is ATC asking me why I am too stupid to fly on a given FL. Sometimes I even fly by Vatscope, rather than my own instruments, just to avoid being interrogated by ATC about my FL mainly during cruise all the time.

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VATScope and SimAware show your true altitude. ATC, when you're in the flight levels, sees your pressure altitude. They will not be the same unless you are in a standard atmosphere with QNH 1013.

You definitely should not fly by VATScope altitude. Prior to the altitude workaround that I added in vPilot 3.3, that was a valid tactic for when you're flying below the flight levels. However, with vPilot 3.3, there is no circumstance under which you should fly by VATScope altitude. Fly by indicated altitude with your altimeter set correctly. This should match what ATC sees. If it does not, then we'll need to look elsewhere for the cause.

Edited by Ross Carlson

Developer: vPilot, VRC, vSTARS, vERAM, VAT-Spy

Senior Controller, Boston Virtual ARTCC

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1 hour ago, Ross Carlson said:

VATScope and SimAware show your true altitude. ATC, when you're in the flight levels, sees your pressure altitude. They will not be the same unless you are in a standard atmosphere with QNH 1013.

You definitely should not fly by VATScope altitude. Prior to the altitude workaround that I added in vPilot 3.3, that was a valid tactic for when you're flying below the flight levels. However, with vPilot 3.3, there is no circumstance under which you should fly by VATScope altitude. Fly by indicated altitude with your altimeter set correctly. This should match what ATC sees. If it does not, then we'll need to look elsewhere for the cause.

Well, this is what I was hoping for with 3.3, but somehow for me it does not work, as explained above. And as I said, even with temperature correction, calculating my true altitude, it does not match what is on Vatscope, but it should, if Vatscope really shows true altitude.

I will do another test, specifically ask ATC what they see and somehow document it. Thanks.

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2 minutes ago, Sebastian Steininger said:

And as I said, even with temperature correction, calculating my true altitude, it does not match what is on Vatscope, but it should, if Vatscope really shows true altitude.

When you say "calculating my true altitude" what do you mean? What are you using to calculate that?

Note that the true altitude sent to the network is equal to what your true altitude would be if the pressure lapse rate in the atmosphere were ISA standard. This is to make it mesh well with other sims that don't simulate temperature affects on pressure. So if you're using live weather, the true alt sent to the network may not match the true alt of your plane in your simulator. For reference, the value sent to the network comes from the "INDICATED ALTITUDE CALIBRATED" simconnect variable, which the MSFS devs added for this purpose. That may differ from the true altitude of your plane in the sim, which is contained in the "PLANE ALTITUDE" variable.

Also, I was told by the MSFS devs that there is still a minor bug in the altitude variables that will be fixed in the next update. This could account for some of the discrepancy, but from my testing, it shouldn't be more than a couple hundred feet.

Developer: vPilot, VRC, vSTARS, vERAM, VAT-Spy

Senior Controller, Boston Virtual ARTCC

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On 4/11/2022 at 1:37 AM, Ross Carlson said:

When you say "calculating my true altitude" what do you mean? What are you using to calculate that?

Also, I was told by the MSFS devs that there is still a minor bug in the altitude variables that will be fixed in the next update. This could account for some of the discrepancy, but from my testing, it shouldn't be more than a couple hundred feet.

ProSim A320 has a built in temperature compensation feature, this is what I am using.

I did another test on Vatsim in "perfect" conditions with a local pressure of 1013, having a private chat open with the controller and he was happy to play it through: indicated FL360. ATC saw FL365, Foreflight FL360 without temp comp.  With temp comp, FL360 indicated, ATC saw FL357, Foreflight showed FL352.

What I do not understand is that Foreflight sees my pressure altitude correctly without temp comp, which in this case with a local QNH of 1013 equals my indicated FL, meaning that MSFS also broadcasts my altitude correctly. How ATC still sees something completely different, is really strange.

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