Force Feedback unflyable?

[Pluto]

....the other night when flying online with a friend, we had the same.
He said he thinks his shaking came from the engine that was not running properly, not from turbulences.
Minutes later he got a failure message, his cooling-water was boiling. Flying behind him I could see steam (or very hot water) trailing behind his plane.
How do you know if the shaking comes from the engine and not from turbulences? He was also just guessing and watching the instruments but when the failure message came, he knew he was right.
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