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Altitude


Donald Stimson
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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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  • 8 months later...

I've to bring up this old topic again as I'm facing the problem of traffic tags on my Navigation Display when flying the PMDG 737 on VATSIM.

During north atlantic crossing I had traffic at FL320 while I was at FL400 and the TCAS gave me a vertical separation of -54 (instead of -80).

Later, as he climbed FL340, I had a difference of -34 (instead of -60).

I'm in contact with PMDG support and a member of the support team told me he'll be asking the devs if Asobo has changed anything.
PMDG support told me that I should try to reproduce this issue over land, so I flew EPMO-EKRN the other day and the issue was still present.

Between me on FL300 and another traffic on FL 370 was +78 instead of +70 and other traffic crossed above on FL350 but showed +56 instead of +50.

 

I had updated the PMDG 737 on 25th DEC and vPilot on 26th DEC. In addition to this, I've opted in to MSFS beta programme on 22DEC but haven't observed this with vPilot v3.4.7 and MSFS beta version 1.30.7.0. for six flights (didn't look for it specifically).


This looks similar to that issue we had about a year ago before vPilot was updated to handle MSFSs pressure and altitude logic.

+56.JPG

THY PL.JPG

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Haven't had this issue in the last few flights, so I think it was something from Asobo's side and not related to PMDG and vPilot.

 

Seems like it's still present. Currently on FL397, TFC below on FL357 (according to vatspy), but ND is showing -36 instead of -40.

Some traffic shows the right difference in alt and some doesnt. 😞

Edited by Reinhard Ziegler
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Super strange is, I'm not having this once with all aircraft and on the other flight with none... I recently had two TFC on my ND at the same time: one was showing -34 and the other one +20?

(Yes, I've checked wether or not they are descending or climbing).

 

I don't even have a clue why this is a (very random) thing right now?

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  • 2 weeks later...

I have to report same strange issue with altitude readings. Today I was able to take this picture. When flying with Fenix A320 I was overtaken by another A320 doing 620knt 🤪 and he was using the same airway. As you can see, both my TCAS and vPilot shows him at the same altitude. But as you can see, he has passed well above my position. I have also checked on your Vatsim map, which showed him at FL364 and my airplane was there at FL 344. 
I have had several strange encounters of this kind, but this was the first one, which I was able to document and get all evidence.

TCAS.thumb.jpg.6e91a4d68f196ef5c3e084f39b7fc81f.jpg

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