It seems like the pressure altitudes within other simulators are diferent to the MSFS2020. This can be seen on online networks like VATSIM. When flying FL390, it is shown as 37.514ft (for example). Users of other simulators at the same leve nearby are indicating 38.999ft.
Also noticed an aircraft at the same FL, is shown on tcas like this. He is flying the CRJ2 in the MSFS2020:
Yes, there must be an error or a conceptual problem in the calculation of pressure altitude. I have noticed that an altimeter change of 1 hPa at FL370 for example results in about 3-times too large change in altitude. It is as if the developers do not know much about this aspect of aviation.
There are two issues at play here. First, VatSpy, the VATSIM website, and other 3rd party apps are reading the altitude from the “plane altitude” simulation variable, which is the airplane’s true altitude, not the pressure altitude. This has always been an issue when above the transition altitude. Unless the sea level pressure is 29.92, the true altitude will be different than the pressure altitude.
The second issue is that MSFS is the first and only sim that takes into account the pressure lapse rate with altitude. This means the airplane’s true altitude will take air density variations into account, so an airplane’s true altitude in MSFS will be different than an airplane’s true altitude in, say P3D, when both airplanes are at the same pressure altitude unless the pressure lapse rate conforms exactly to the standard day lapse rate.
There are some rather lenghty threads at the VATSIM and flightsimulator.com forums adressing this issue:
Ross Carlson, developer of vPilot, is aware of it and as far as I can tell, he’s in progress of adapting some things in the background. MSFS is handling pressure the right way, every other simulator does not
Anyone know why there are inconsistencies? I have been in multiple planes where I noticed the altitude was off, but then later on I would be in the same area and the altitudes would be correct, even sometimes when I was in the same plane when previously it was reading incorrect altitude.