During my long and stable cruize, my 747 suddenly changes speed. As a result I'm overspeeding or stalling my plane. For eg from 300kn to 480kn.My aircraft is a little shaky then. Is this just windsheer? Such a extreme speedchange can't be normal.Something I 'm doing wrong?Thanks,Martin

The MSFS wx engine has a problem with sudden shifts in wind speed/direction and pressure changes. See if the problem happens with clear wx checked (no weather), probably not. Get a registered copy of FSUIPC and use it to dampen the weather.