VATSIM / IVAO / PILOTEDGE Users - Be aware of an important bug!

That’s probably separately fetching the pressure (wrong) altitude and the GPS (correct) altitude via SimConnect, so it’ll naturally reflect the altimeter on the pressure altitude readout.

When using an actual barometric pressure calibration, I always get results that start about accurate at ground level and get worse the higher I go, which matches the original description of the bug and the pre-hotfix behavior.

I would assume that VATSIM clients fetch the GPS altitude, which would be most similar to actual ADS-B or ground radar data.

It may depend on the client then? Smartcars is definitely fetching the wrong pressure altitude. I’m learning as I go with this bug.

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Darn. If it’s not in a hot fix then it’s a bigger problem than they thought or it’s just not a priority. That’s disappointing.

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I have the same problem at the beginning of flight, Standard Baro i am at 32,000ft with CRJ4 on IVAO flying from KAVL to KEYW, on webeye i seem on 33,500ft but after a while webeye shows 32,200 which is normal also same change on SIMACARS, strange.

Definitely not fixed. ATC still telling me to expedite my climb even though i’m already at that altitude and even confirmed baro is set correctly by pressing B.

Nope. Not fixed at all. If anything, it’s worse. Did they even bother testing this?

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Yep. Not fixed. Doesn’t anyone do some tests before release and writing release notes. Amateurish.

If I let my team roll out code of this caliber, I would have been out of a job a long time ago.

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It seemed to go way off on altitude once I switched to standard pressure at FL180. Live weather temps still all over the place.

It’s very unfortunate the hotfix didn’t resolve the problem. Hoping we can hear some more from the team about what’s up.

Hey @Bishop398 - can you please comment on this as I know you mentioned a fix was coming… guess it didn’t happen in this patch?

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@moxiejeff The fix was part of this patch, yes. The temperature data seems to be affecting the fix and I’m unsure as to why the altitude temperatures are not resolved. A good number of hours of flight time was spent testing the temp fix and this behavior was not observed.

For now for online flights I would still recommend Clear Skies. That’s all the information I have at the moment.

-Matt | Working Title

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GPS altitude (in a real aircraft) is true altitude above sea level which is almost never the same as indicated altitude. They would only match if conditions (both pressure and temperature) were exactly ISA.

I will verify this tonight using the sim var watcher, but what I think is happening is that the simconnect variable INDICATED ALTITUDE (which should always match whatever is shown on the altimeter) is now receiving the value of either pressure altitude or true altitude. AFAIK, INDICATED ALTITUDE is the simconnect variable that external client programs for VATSIM have always used.

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Interesting, I had thought that the altitude calibration given by the airport compensated for both pressure and temperature at ground level, in which case I’d expect differences only if there were pockets of different temperature and pressure between the airplane and the ground. Guess I was wrong!

I’m a bit surprised though, since the difference from GPS altitude is showing up in my tests so far at about 50 feet per 1000 feet (500 feet off at 10,000 feet). That’s a much greater difference than I expected.

Do you know if real-life ADS-B reports pressure altitude instead of GPS altitude as well?

This presumably means that you can’t accurately tune the barometer by dialing in the known elevation of the airport, either, without doing manual calculations for the temperature. Is this correct?

This is actually exactly the case. Right now, you should definitely observe that field elevations once baro is set should be correct, which was not the case prior to the patch (they could be off by potentially 1000+ ft). I believe the wrong temperature data is causing a number of issues above that, though.

-Matt | Working Title

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Ok, did some checking on the source for fs2ff and the “GPS altitude” I receive in ForeFlight is pulled from the SimConnect variable “PLANE ALTITUDE”. This is higher than the altitude reported on the altimeter (in my testing in daytime in Southern California summer, by 500 feet at an indicated altitude of 10,000).

At the airfield they both match.

I think it’s PRESSURE ALTITUDE which Vatsim uses since INDICATED ALTITUDE is always what’s in PFD. So even if you fly at FL300 with baro 993 hPa INDICATED ALTITUDE will show 30000ft, but PRESSURE ALTITUDE shows 32000ft or so.

When ISA is OK, INDICATED ALTITUDE and PRESSURE ALTITUDE is close each other. But when ISA jumps to +65 INDICATED ALTITUDE will still show “correct” altitude, but PRESSURE ALTITUDE is way wrong.

Volanta for example reports PLANE ALTITUDE

Here’s couple screenshots from FL300:

+6 ISA

+57 ISA

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I departed Colorado Springs and yes the displayed altitude matched field elevation and everything was reporting correctly in VatSim, STKP & Volanta (~6,100ft), where before it would be off.

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The thing that strikes me here is that ambient pressure has somehow not really changed even though the temperature is way higher. That’s going to really throw the whole thing off, that data just doesn’t make sense. In the two shots, the difference between real altitude and pressure altitude only changed by like 12 feet (which I would expect given the small ambient pressure change). So some data is totally wonky.

-Matt | Working Title

When I stopped climbing to FL300 ISA was +57c and when it changed to +6c, Ambient pressure spiked to 312 along with the altitudes, then slowly started going lower. I think I took the +6c screenshot bit too early, Indicated altitude and Ambient pressure was same after a while than in +57c screenshot, Pressure altitude and plane altitude was different and temperatures of course between the two screenshots.