Hello,Not sure why this is happening but sometimes ill be able to do a flight perfectly without anything happening. Others, i will be at fl390 or fl320 exc and i will randomly either stall or descend then slow WAY down... I usually use a cost index of 100-150 when i fly and get no FMC messages during the flights. The plane also fights to stay at the altitude it descends to, the nose is pointing up 10 on the attitude indicator. This time it did it to me when i was on a short flight from Seattle to San Francisco. I was at 390 and then it descended to 313 and slowed down to about 170kts or somewhere around there. Im not sure if the plane stalled or not, i was making some food in the kitchen then came back and that's where i was.Something im doing wrong? O_o

I hope to god thats not your name... pls sign your real name.Ok you don't mention Aircraft type, ZFW, GTOW, Optimum crz alt in the FMC, are you using LNAV VNAV or are you using FLCH V/S etc etcRob

this is it lolusing the 747. had lnav and vnav on at the same time.

Yout parents must love you... Anyway pls post a screenshot. it will be the fastest way to figure out what your doing wrong.Rob

I saw somewhere in this forum where some folks were experiencing the same behavior when they are you're using the internal FS weather engine with the "Disable turbulence and thermal effects on aircraft" (- on the Weather tab in option) NOT checked. Give it a try and see if it helps.Bob

FS real-weather is weird. It appears the atmosphere disappears sometimes!Best regards,Robin.