Originally Posted by
compressor stall
All interesting theories about multiple coincidental failures.
But honestly, the most likely scenario that fits the wreckage trail and aforementioned witness accounts is the Somatogravic Illusion. Look here
https://www.atsb.gov.au/media/5226668/199003089.pdf
Somatogravic alone in an experienced pilot, even in fog unlikely (but not impossible), I think most would agree.
Aircraft likely to have a mix of electrical and vacuum instruments, so no single failure likely to take all out.
But here's a thought. A while ago, picking up my Aztec from maintenance which had over-run, having not flown for over a month (due to said maintenance). I watched the airspeed slowly drift back as I climbed over the upwind end of the runway. It had been fine increasing on the runway. Altimeter and VSI indicated I had stopped climbing. I checked throttles and props and pushed everything forward and checked engine instruments and all seemed (and sounded, as far as I could recall) normal but I was aware if something was wrong with engines manifold might be close to atmospheric and props might be turning at governor speed but not absorbing much power. I worried about stalling but it felt (as far as I could recall) to be flying ok. I diagnosed it as a pitot/static issue guessing something had moved into the system (insects later found) and confirmed GPS ground speed was credible and completed a circuit using GPS ground speed and visual reference.
Now if there was a problem with pitot/static system (I assume King air has twin probes etc, but both could have been blocked, or covers left on or something had worked into common piping) causing similar symptoms, falling airspeed, erroneous altimeter reading, coupled with sense of climbing in fog with no visual reference, there would be a strong tendency to push nose down.
Yes the AI might show level flight but if the AI says you're level, which it probably would do anyway if it failed, and your senses and ASI are telling you you're over pitching and about to stall, which do you trust instaneously while you figure it out?
Easy to say from here keep climbing but you can't see the ground in fog, you do know that if you stall you won't climb, you want both airspeed and height. In fog immediately after takeoff the problem might not be so apparent.
As I say, just a thought, prompted by the somatogravic suggestion. If it's not helpful please feel entirely free to disregard without pointing out my idiocy!