Date: 201505
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Weather elements / visibility: Fog; Turbulence; Snow; 10
Aircraft: Bonanza 36
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Altitude Hold/Capture
Reporter organization: Personal
Reporter function: Single Pilot
Reporter qualification: Flight Crew Multiengine; Flight Crew Commercial; Flight Crew Instrument
Human factors: Situational Awareness; Fatigue; Confusion
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Inflight Event / Encounter Weather / Turbulence; Inflight Event / Encounter Loss Of Aircraft Control
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Took Evasive Action; Flight Crew Regained Aircraft Control; Flight Crew Became Reoriented
Contributing factors: Aircraft; Human Factors; Weather
Primary problem: Human Factors

Narrative: Cruising on Autopilot (AP) at 9;000 direct ZZZ1 about 30 nm southwest of the VOR; I asked ATC for a deviation to the right to avoid an area of heavier precipitation; which they called out to me and I could see on my [GPS weather display].  Once clear of that heaviest area; I turned back north direct ZZZ1; and from ZZZ1 turned direct ZZZ2.  I had been in and out of the bottom of the ceiling at 9;000 MSL; no ice and mostly smooth.   Near ZZZ1 I started to encounter a lot more turbulence and entered solid IMC; in snow and clouds but still no icing.  I was keeping an eye outside to watch in case I needed to ask for lower if evidence of icing began.  ATC called and asked me to maintain 9;000 and repeated the altimeter setting; and I scanned and saw that I was descending through 8;600 MSL; and that the AP had turned off; probably due to the turbulence.  It does have an alarm when this happens but I did not hear it.  At that point I raised the nose to climb back to 9;000; but when I looked over at the Airspeed Indicator (ASI); it was dropping rapidly below 80 knots.  Not wanting to stall in IMC; I lowered the nose substantially.  At this point my scan was uneven and not making sense. I have read a lot of accounts of pilots who are rapidly overcome in situations like this. At that point I decided that the safest course of action would be to continue to descend rapidly to what I knew was warm VMC below me.  I lowered my landing gear; started a rapid descent to around 4;000 MSL; where I broke out of the snow and clouds and could reorient myself.  ATC advised me of closest local airports and asked about assistance; I asked them to stand by.  Once I was back in control and everything was looking normal; I flew on for a while; and continued on to my destination at 7;000 MSL; which from that point would keep me in VMC.  ATC asked me about the nature of the problem and I told them that I lost my AP in IMC and had loss of control.It is clear in hindsight that the reason I was seeing the drop in the ASI was that the pitot was being plugged with ice or snow or water.  I should have had the pitot heat on but did not.  The rest of the instruments could have shown me that; if my scan had been good; but I was only intermittently scanning while the AP was flying in cruise.  While my reaction was certainly a way to stay safe; it may have been an overreaction.   However; I was tired after a long day and knew I was not at my best; and I wanted to get somewhere safe quickly.  I was far from any busy airspace; and [advising ATC] and descending did not cause a scramble to move other aircraft; as far as I know.




Synopsis: A BE36 pilot reports encountering snow and turbulence at 9;000 feet causing an autopilot disconnect that is not noticed. ATC does notice and a climb back to 9;000 is initiated before very low airspeed is detected. A rapid descent to 4;000 feet is initiated and ATC is advised. Lack of pitot heat was the likely cause of the low airspeed indication and the flight is able to continue to destination.