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martinlest2

Altitude Discrepency

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I thought this problem had been posted before (surely?) but none of the searches I have done have showed up a thread, so...Would anyone know why so often there is such a big difference between the altitude shown on my flight instruments (and in FSNavigator) and what shows up in the onscreen data (from Shift+Z). At the moment, according to my PMDG 737 panel (though it happens in all a/c) I am at 30000' - QNH showing 29.92 STD. FSNavigator agrees. But the onscreen data shows me almost 500' higher - and ATC will often (though oddly not always) pick up on this and tell me I am too high and to descend.Anyone know what is going on and if it's fixable?Martin

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"have showed" (???!!) ... er, 'has shown', I meant. How did that get typed? As an English teacher, I just HAVE to correct it!!(Moral: Read what you write before you press the 'post' button!)M. :(

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martin:if the local pressure is of greater difference from standard you can see altitude differences greater than 500'.FS ATC isn't smart enough to know that everyone is still flying the correct flight levels.--

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Er, I'm afraid I don't understand that. Up at 30000' surely 29.92 is set as standard? Is this just a bug in FS?M.... if the local pressure is of greater difference from standard you can see altitude differences greater than 500'.

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Er, I'm afraid I don't understand that. Up at 30000' surely 29.92 is set as standard? Is this just a bug in FS?M.
to confirm theory:setting standard after transition altitude does not mean that the world's pressure is now 29.92. aircraft at altitude are only at FL350 = 35,000' when pressure is actually 29.92. if the local pressure is +/- aircraft at also +/-. as all aircraft are using the same setting, 29.92, all are at the same 'relative' FL350 ... even if not at 35,000'.FS's ATC doesn't look at flight levels. the sim looks at actual altitude. if the local pressure is significanly away from standard (-/+) you are therefore, according to FS's ATC, busting an altitude. FS ATC is dumb.--

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FS ATC isn't smart enough to know that everyone is still flying the correct flight levels.
All due respect, I think they are. The only time I get busted for altitude deviation is when I forget to adjust the altimeter at transition altitude. I always let the AP control altitude when flying in the levels.Martin, Shift+Z will show you actual altitude above sea level. Your altimeter shows you pressure altitude which is adjustable to local pressure settings. Since there is no practical way to measure the air pressure at all the different altitudes planes fly all over the world we use the standard of 29.92 above FL180. This way, as Scoob said, all planes use the same setting, so will all have the same variation between pressure altitude and actual altitude. BTW, ATC gets your altitude from your transponder which typically gets that info from your altimeter. As long as that is set to 29.92 above FL180 you should be OK.
FS ATC isn't smart enough to know that everyone is still flying the correct flight levels.
All due respect, I think they are. The only time I get busted for altitude deviation is when I forget to adjust the altimeter at transition altitude. I always let the AP control altitude when flying in the levels.Martin, Shift+Z will show you actual altitude above sea level. Your altimeter shows you pressure altitude which is adjustable to local pressure settings. Since there is no practical way to measure the air pressure at all the different altitudes planes fly all over the world we use the standard of 29.92 above FL180. This way, as Scoob said, all planes use the same setting, so will all have the same variation between pressure altitude and actual altitude. BTW, ATC gets your altitude from your transponder which typically gets that info from your altimeter. As long as that is set to 29.92 above FL180 you should be OK.

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Hi,What I was saying is that pressure is set at 29.92 above transition - no, I didn't think that the pressure suddenly WAS actually 29.92 as soon as you hit 18000', and all altitudes thereabove.The 'problem' in FS9 is that with pressure set at 29.92 over 18000', my instruments show me at, say, dead on 35000' but ATC still sometimes tell me I am 300' above my assigned altitude, so to shut them up I have to fly at what looks like 34,700 on my instruments, or perhaps a bit higher, as there is of course a couple of hundred feet either way allowed before ATC starts complaining.Well, it's not a huge problem, but in the real world if I am assigned an altitude and stick to it according to my instruments, I never get ATC complaining, as in FS9. But then as I only fly little single engine jobs, I never get anywhere up near transition altitude!M.

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In my experience, FS's ATC does see Flight levels. I fly with real-world weather all the time via Active Sky and have never been called out while on the standard (29.92) setting. What Martin is talking about, as best I can understand, is that the altitude reported in the data line (Pressing Shift-Z) is different from that reported on the aircraft panel. If that is the case, I'm pretty sure that the data line always shows the true MSL altitude regardless of altimeter setting on the panel.

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