I fly the 2008 Maddog in FSX using Active Sky Evolution. On a typical flight, I am decending in vertical speed mode at about -1800 fpm. Suddenly, for no apparent reason, the vertical speed mode will change from -1800 fpm to around +5000 fpm and before I can correct it I will gain about 3000 ft of altitude. I then reset the vertical speed to -1800 fpm and all goes well for awhile, and then the same thing happens again.I tried decending in VNAV, but the problem still occurs. I am using FSUIPC to control the wind, pressure, and temp shifts. I have cloud turbulence, cloud icing, wind turbulence, wind shear, thermals, and downdrafts all set to 0 in ASE. I am not using DWC, and I also have dynamic rate of change at 50% and download interval at 15 mins. Is this caused by sudden pressure or temp changes? If so, anyone know how to deal with it?

Hi,No ideas form me. I can suggest a different plane just to compare.

Thanks Jim. I think I solved it. I clicked on the "Thermals" tab, and I noticed that there were 5 thermals saved there. I didnt create them so I deleted them. Did a few more flights, and so far I havent had any more problems.