Is their anyway to stop it going back to normal speed every time there's turbulence? I don't really want to have to turn active sky off so hoping for other solutions!

If I understand correctly your question, I assume you are using the acceleration mode of the PMDG FMC, in this case what you are experiencing is normal and was a welcome refinement brought by the PMDG team, when you notice that it throttles back to normal sim speed, it is meant to avoid unruly behaviour caused by turbulences or sharp turns on the route when on A/P, that would induce unrealistic fluctuation in attitudes and/or changes of altitudes. However, it will/should get back to the acceleration mode you selected as soon as the disturbance factor disappears. In case of persistant turbulences, it may take a while before it accelerates back to your selected value.

If you absolutely want to avoid any fluctuation, you should use the sim acceleration mode that will ignore any of the above factors, but in case you hit severe turbulences or have to turn left or right on autopilot, your plane might become difficult to manage and will wave madly around its altitude and headings, it's your choice really.

In case this does not resolve your issue, it would be better to post this question in the PMDG forum where you will find proper assistance.

Edited May 1, 20188 yr by Jean-Claude