I'm in flight now in DF737 at FL300. As I fly and data is updated, my plane climbs and descends according to pressure changes. Since I have my altimeter set at 29.92 over FL180, shouldn't my plane stay at the same altitude? I played with the QHN transition rate, putting it to 100 to slow changes. How does pressure affect a plane's alt over FL180? I assumed it would stay at the same altitude.Any info would be great!Thanks, Adam :-zhelp

Hi Adam,When you're flying above FL180 and using 29.92, in real life the pressure obviously varies but it happens very slowly. The whole basis for using 29.92 is to have every pilot using the same setting and thus flying at the same altitude index although this will NOT usually be the actual altitude. Let's say local surface pressure is reported at 30.42. Every inch of mercury change = 1000ft altitude change so if you are set at 29.92 and flying at indicated FL200 you are actually flying at FL205 (.50 inches = 500ft). Likewise, if local altimeter was 29.42, you would now be flying at FL195. What happens in the sim is that as you fly between areas of different pressure, the altimeter will climb and descend even though you may be at a constant altitude. In real life this happens so slowly, and the altimeter is your only reference, so you don't notice... but really you are making the aircraft SLOWLY climb and descend to keep that indicated altitude centered. In the sim it tends to happen faster and 'choppier' so you will notice a jump in the altimeter even on the smallest change (.01 inches, or 10ft). Try playing with your transition rate, and maybe try FSUIPC's pressure transitions as well. Get them as slow as possible but even then remember that the smallest change in the SIM (.01 inch) will make that altimeter jump 10 feet!Hope that helps..-Damian Clark

Thank you very much Damian for the info. It was very informative. I will take your advice and try the settings. I use your program too! It's wonderful!:-smile12 Just new to this add-on weather stuff. Gonna have to do some learning/tweaking. I feel honoured to have you respond to my query!Thanks again,Adam