It's been a long time, but in addition to any issues with your altimeter setting I *think* I might have added code ~8 years ago to simulate the effect of temperature on altimeter readings. In real life, even if you have exactly the correct altimeter setting for the ground below you, and the altimeter is perfectly calibrated, your altitude can be off by hundreds or thousands of feet from what you see on the altimeter.
Generally speaking, you'll be lower than you think if the temperature is below ISA, and higher than you think if the temperature is above ISA, because temperature affects how much the air pressure changes with altitude. The altimeter is calibrated to assume 15 degC at sea level and a perfect consistent temperature gradient above that. All the best, David In Canada, we're required to increase minimum altitudes for approaches, etc., when temperatures are cold. We also have designated mountainous regions where you have to fly higher in the winter. On Sat, May 29, 2010 at 1:02 PM, Rob Shearman, Jr. <[email protected]> wrote: > Hi there -- > > Recently while flying with the MD-81 at cruise levels of FL330 or so, I > noticed there were some significant discrepancies between the displayed > altitude and the altitude found in the property tree at > /position/altitude-ft. I was able to observe the same problem in the > 777-200ER -- I flew a flight at 33000 and the Flight Tracker reported my > altitude at close to 35000. So the discrepancy at cruise is as much as > 1000-2000 feet sometimes, even when using the altimeter setting reported in > the METAR (which, of course, you're not supposed to do above 18,000 in the > U.S., but for testing purposes I did so to see if it accounted for the > error). > > However, today loading up my custom ATC scope I observed a discrepancy in > altimeter readings which may account for the problem. > > http://i289.photobucket.com/albums/ll209/rmsjr1974/altimeter-discrep.jpg > > Notice in the shot that the METAR is reporting 29.94, but the property tree > and the scope panel are arriving at 29.90. I presume at high altitude this > discrepancy would account for differences in the gauge reading. > > This is with the 25 April CVS build, so if altimeter code has changed since > the migration to git, I apologize in advance. > > Thanks, > -R. (MD-Terp) > > Robert M. Shearman, Jr. > Transit Operations Supervisor, > University of Maryland Department of Transportation > also known as [email protected] > > > ------------------------------------------------------------------------------ > > > _______________________________________________ > Flightgear-devel mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/flightgear-devel > > ------------------------------------------------------------------------------ _______________________________________________ Flightgear-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/flightgear-devel
