Coincidentally in the March edition of Pilot magazine the ILAFT column tells the story of a Piper Malibu flight from Rotterdam to the UK with a commercial pilot in the left seat and an experienced instrument rated pilot with 1,500 hours in the right hand seat. Having descended into the UK they levelled off at 2,400 feet in IMC conditions using the autopilot but forgot to add power and very nearly stalled. The non-professional pilot in the right hand seat realised and added power a few knots above flap up stall speed having suddenly noticed the ASI unwinding rapidly. That is always a trap when descending and using an autopilot for heading and altitude capture but manual throttle. Because the autopilot is engaged it can give a false sense that all is under control.
There are several possibilities for what happened to Sala’s plane but the above error is certainly a possible candidate aided by ice distraction and night IMC.