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The custom atmosphere simulation means the aircraft will fly at the indicated altitude for the conditions, which is quite different from the perfectly correct altitude that most simulations use. This may cause confusion for online controllers as your aircraft will appear to be off altitude. Please familiarise yourself with the atmosphere simulation fully before flying online.

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Edited by Graeme_77
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I just noticed something odd, if Xpilot is looses Vatsim connection, the altitude changes drastically despite this not being ticked. This happens regardless of weather injecting addon (testes with XE, ASXP and NOAA) +- 800ft

Edited by jakobeng1303
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15 minutes ago, jakobeng1303 said:

I just noticed something odd, if Xpilot is looses Vatsim connection, the altitude changes drastically despite this not being ticked. This happens regardless of weather injecting addon (testes with XE, ASXP and NOAA) +- 800ft

I don't have the aircraft but the behavior seems correct -- you probably understood it backwards. When the checkbox is ticked, altitude will not change  (because advanced barometric altimetry is always on); when it's unticked (your case: advanced barometric altimetry enabled when offline only), when you lose connection it switches from the online/simplified simulation to the realistic one, hence the altitude change…

Some observations for developers:

- assuming it isn't already, online networks would probably appreciate if the realistic mode were disabled by default (fewer support headaches)

- maybe the realistic system could be on a delay to account for the occasional lost connection, or maybe even remain on the simplified system if the connection is lsot in the air

- maybe the transition from the simplified to the advanced simulation could eventually be more gradual to avoid an 800ft-like jump while airborne?

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The system is on by default because a lot of the advanced features like SBAS / Baro VNAV approach selection only make sense with the temperature effects, and this feature set would be rendered useless with the atmosphere simulation off.

There may be some changes possible to inhibit altimetry changes when in-flight to deal with the vatsim disconnect case, I'll ask the devs to look at that as a possibility such that once you're airborne, you don't get atmosphere changes.

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54 minutes ago, Rodeo said:

you probably understood it backwards. When the checkbox is ticked, altitude will not change  (because advanced barometric altimetry is always on);

that amkes a lot of sense, thank you. It thought that it was opt in only and would be entirely avoided if not selected

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Posted (edited)

Just to explain the issue clearly. In real life altimeters suffer from "errors". When it says 10000ft it doesn't mean you're 10000ft above the sea, it means in the conditions the altimeter was calibrated for, if the subscale (baro) was set perfectly, you'd be at 10000ft.  On a cold day you could be at 9000 "real" ft, on a warm day 11000 "real" ft. But the altimeter would still show 10000ft.

Now all real aircraft fly in the same real sky, so on a given day, one aircraft indicating 10000ft and another aircraft indicating 11000ft will pass each other safely. Even if their altimeters say 11000ft and 12000ft respectively. 

The Challenger 650 simulation includes these altimeter effects. Unfortunately when reading the information from X-Plane, online network clients read the "real" altitude (to draw the aircraft) and importantly (and unfortunately) show that to the controllers. This does not happen in real life, as controllers and transponders have no secret data from the world. This means online controllers will see an incorrect Flight Level reading when the Challenger 650 is doing an accurate simulation of real altimetry. 

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To prevent any issues, the Challenger 650 simulation includes an option to disable accurate altimetry for flying on line. If you disconnect from the network, the Challenger will resume simulating altimetry effects, and as a result may climb or descend. 

It's the hope that in the future online networks will read two separate values, one "real" altitude to draw the various aircraft in the 3D world, and one "sensed" altitude, to downlink to controllers for the Transponder / SSR altitude. 

More information on altimeter errors https://skybrary.aero/articles/altimeter-temperature-error-correction

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Edited by Graeme_77
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I have disabled this feature as recommended for online flights, however ATC is complaining that I maintain 300-600ft below my assigned altitude, despite me having QNH1013 set. This is despite another xplane user (flying another aircraft) infront of me being on almost the exact same altitude, without any issues there.

Looking on software such as VATSpy, I can see both me and the aircraft ahead is indicating for ex 28700ft, but ATC only complains about me.

Again this is with realistic temperature effects disabled.

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There is a minor issue with the altimeter information in the initial release of the 650, that is being corrected for the next version. It's also separate from the altimeter temperature effects, and doesn't change anything in the first post on this thread.

Let me explain the issue first:

In real life, traditional ATC "primary" radar has no way to see how high an aircraft is, so a system called "secondary surveillance radar" or SSR sends a radar pulse to interrogate the aircraft transponder. The transponder provides a Mode A code such as "4651" and a Mode C response encoding the aircraft altitude. Modern SSR does loads more with Mode S but let's stick to the basics.

Real Mode C altitude responses are fixed to 29.92inHg for the encoder pressure setting - it's basically always reporting a flight level, even at very low altitudes. To present that correctly, the controller radar display reads the 29.92 altitude, and converts it into whatever the sector pressure is. So if a controller tells you "Palm Springs Altimeter 3014", their radar display is converting the 29.92 into the correct altitude for 30.14.

Now, in online flying this doesn't work. I could be flying on my own fixed weather, another pilot could be flying real world weather, and yet another on another sim with a slightly different weather source. To make this work, rather than sending the altitude relative to 29.92, the “xPilot” VATSim client sends the actual altitude displayed on your altimeter. If it's right for the pilot, it's right for the network. (I'm not talking about the altitude to draw the 3D aircraft model here, that's something else, I'm talking about what shows on the controller's display). 

The advanced systems in the 650 operate entirely separately from X-Plane. On the initial release version, the X-Plane stock cockpit altimeter is not synchronised with the Challenger 650 cockpit, so when, for example, the Vatsim client asks for the cockpit altitude to show the controller it's linked to the X-Plane cockpit values and not the Challenger 650.

This will be addressed in a future release, but for the time being the keyboard binding "Baro pressure selection 2992" can at least set X-Plane to the standard pressure setting. It won't fix the issues in every case, but is a workaround until the product is updated.

Sorry for the inconvenience to online pilots - the Challenger 650 is pushing the boundaries of what X-Plane can do, so it's only natural these previously unknown issues are exposed as more and more people enjoy the Challenger 650. 

Edited by Graeme_77
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22 hours ago, Graeme_77 said:

There is a minor issue with the altimeter information in the initial release of the 650, that is being corrected for the next version. It's also separate from the altimeter temperature effects, and doesn't change anything in the first post on this thread.

Let me explain the issue first:

In real life, traditional ATC "primary" radar has no way to see how high an aircraft is, so a system called "secondary surveillance radar" or SSR sends a radar pulse to interrogate the aircraft transponder. The transponder provides a Mode A code such as "4651" and a Mode C response encoding the aircraft altitude. Modern SSR does loads more with Mode S but let's stick to the basics.

Real Mode C altitude responses are fixed to 29.92inHg for the encoder pressure setting - it's basically always reporting a flight level, even at very low altitudes. To present that correctly, the controller radar display reads the 29.92 altitude, and converts it into whatever the sector pressure is. So if a controller tells you "Palm Springs Altimeter 3014", their radar display is converting the 29.92 into the correct altitude for 30.14.

Now, in online flying this doesn't work. I could be flying on my own fixed weather, another pilot could be flying real world weather, and yet another on another sim with a slightly different weather source. To make this work, rather than sending the altitude relative to 29.92, the online clients send the actual altitude displayed on your altimeter. If it's right for the pilot, it's right for the network. (I'm not talking about the altitude to draw the 3D aircraft model here, that's something else, I'm talking about what shows on the controller's display). 

The advanced systems in the 650 operate entirely separately from X-Plane. On the initial release version, the X-Plane stock cockpit altimeter is not synchronised with the Challenger 650 cockpit, so when, for example, the Vatsim client asks for the cockpit altitude to show the controller it's linked to the X-Plane cockpit values and not the Challenger 650.

This will be addressed in a future release, but for the time being the keyboard binding "Baro pressure selection 2992" can at least set X-Plane to the standard pressure setting. It won't fix the issues in every case, but is a workaround until the product is updated.

Sorry for the inconvenience to online pilots - the Challenger 650 is pushing the boundaries of what X-Plane can do, so it's only natural these previously unknown issues are exposed as more and more people enjoy the Challenger 650. 

Glad to hear, I was starting to get really annoyed by Ze Germans making me explain "Warum Ich bin flying at +200". 

Anyway, we're sorry to make you inhibit your complicated altimeter simulation. Maybe soon it will become standard in XPlane (12 maybe?) ! 

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