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I always find it irritating when I'm at CRZ, let's say FL320 and Vatsim/ProjectFly or any other flight tracking shows 32322FT or 31998FT. I know these programs gets there data from the TRUE ASL altitude in the sim. Is there anyway to lock it? So when my aircraft altimeter shows 32000 this is also shown in flight tracking

As per real world, I've "heard" the mode C altitude encoder is "fixed" at all time, so it seems real aircrafts displays fluctuations in it's altitude like the sim but gets lock by an encoder to show fix altitude for EG on FR24 32000FT 33000FT 34000FT ETC

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I don’t fly with online services but the reason you see a difference is because the software reading your altitude doesn’t know about Transition Altitudes and Levels. Until they do you will continue to see a difference.

There’s no such altitude as 32000ft. Anything above 18000ft in the US is classed as a Flight Level. So that would be FL320.

The rules in Europe differ from country to country.

Edited by Ray Proudfoot

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As Ray says, the sim outputs your true altitude MSL but you are obviously (and correctly) flying a Flight Level.

This makes sense in many ways because VATSIM (for instance) needs to know your true position in space so as to plot your aircraft's location correctly for other pilots.

However, it is basically the opposite to how a real Mode C encoder works; the transponder generally always transmits the aircraft's Pressure Altitude (i.e. the reading that would be indicated on the altimeter when the sub-scale is set to 1013 hPa). This means that it will always read flight levels; so as you say, at FL350 the transponder and the altimeter will match up: at lower levels, however, there will be a difference if the QNH is different to 1013.

It is possible for software reading your altitude to correct it for QNH as the current QNH in-sim can be read through Simconnect/FSUIPC and the appropriate correction applied for display purposes. As I say, it wouldn't really make sense for VATSIM as the pilot client needs to know your true altitude (ATC clients generally apply the correction to your indicated altitude based on the QNH so controllers will see you indicating FL350 rather than FL354); but there's no reason ProjectFly, for instance, couldn't correct it but it would have to be done within their tracking software which connects to your sim.

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