Hello, I have been trying some great circle routes recently that go near the arctic areas, or at least along the northern coasts of Canada. Flying the pmdg 747-400 for fsx.I've noticed that sometimes I will suddenly get a warning from the FMC saying something like "MAX ALT FL210". It seems like I enter a very strange pressure area and have to reduce altitude significantly in order to get any thrust from the engines. Otherwise I just tend to slowly lose airspeed until stalling out. It doesn't usually seem to be accompanied by particularly bad weather or anything. (edit: other than it is usually at latitudes over 68-70)I'm curious if someone knows what phenomenon causes this? Is air pressure significantly different in pockets very far north? Is there a good way to plan for fuel usage on these? When i hit them a lot of times I will get a low fuel warning as well from the FMC, but once i get past them the calculations generally return to showing similar values as what I had before. I'd like to plan for the extra time spent descending or climbing though. Do i need to add more waypoints in those areas to try and see more accurately from METARS if there are significant drops in pressure, is there something specific to look for?Thanks,-andy crosbyedit 2: this is with "real world every 15 minutes" weather in fsx

I've flown the polar routes without this, and don't think your problem has to do with latitude.However, I have had this happen after changing focus from the simulator to the map or some apps (but not all apps). The fix is to reset the FMC by pressing VNAV once or twice. It is some kind of glitch that is reproducable but only mentioned occasionally here.

Hehe, The warning message fooled me into thinking something was going on for real. Thanks, I'll try that trick next time it happens!-andy crosby