What a shame. Latest news reports that divers are being sent to recover the body. I don't know yet who the pilot of that plane was, but I know several of the pilots who have been ferrying those over to Russia over the past couple of months, so I'm sure I know him.
Looking at the
track log, my best guess would be that he got loaded up with ice, and got pretty slow trying to maintain altitude and then probably stalled. All the data after 10:49 looks erroneous, but before that it looks like he had been slowly climbing to 5,500 and then leveled off for about 5 minutes, with a ground speed of 53 knots. Winds aloft for that time show the winds at 040 at 14 knots with an OAT of -7C. That would put him in level flight with a TAS of 67 knots which would be about 62 knots IAS , which is pretty slow for an iced up airplane with an extra 125 gallons of AvGas in the back seat. Without ice and at full power, a 172S will still do about 120 knots TAS with a full ferry tank in the back. If he was running at full power, that would have been a ton of ice to slow him all the way down to 67 knots. Needless to say, in a situation with an iced-up, overgross, and aft CG aircraft, the stall speed is going to be much higher and if the aircraft does stall, it is most likely not going to be recoverable.
Obviously this is all speculation, but all I can say is that airframe icing is serious business and should be treated as such. I think this goes to show how quickly a situation can go from bad to dead.
My condolences go out to the pilot's family and friends.
Blue Skies!