Hello,   today I had a loose of speed midflight from EDDF to ESGG and the plane started to descent. I already had reached the cruising altitude. With a SAT -48 / TAT -37 and no visible moisture I would rule out icing. This is the state during the started descent:

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  So I disabled the AP and took over the control of the plane. I noticed that the stab trim has some very high value (around 14). So i corrected the trim and the plane stabilize