Date: 201307
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: IMC
Weather elements / visibility: Icing; 0
Light: Daylight
Aircraft: M-20 Series Undifferentiated or Other Model
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Descent
ATC / advisory: Center ZZZ
Aircraft component: Elevator Trim System
Component problem: Malfunctioning; Design
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Private
Human factors: Workload; Situational Awareness; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action; General Maintenance Action
Contributing factors: Aircraft; Weather
Primary problem: Ambiguous

Narrative: I was flying eastbound at FL250. Outside air temperature was -10 degrees Celsius. In the thin air; I fly on autopilot using GPS steering and altitude hold. At around 500 miles out from my destination airport the jack screw which adjusts trim froze up. This prevented my autopilot from being able to adjust trim and hold altitude. I was in VMC at the time. I then hand flew the altitude and let the autopilot steer the plane. An hour later; I entered into IMC conditions. I was still flying the altitude by hand for the next 45 minutes. I worried about potential icing and requested a descent down to 17;000 MSL. I figured that the descent of 8;000 FT would change the temperature to +6 degrees Celsius or 2 degrees per thousand FT; the adiabatic lapse rate. The temperature went to 0 degrees Celsius and I began to accumulate ice. It was rime ice on the leading edge of the wing along with the windshield icing up. I had pitot heat and propeller boot heat on so no issues with the instruments. I informed Center I was taking on ice and asked for 15;000 FT MSL and I was still on an IFR flight plan. As I leveled out at 15;000; the ice started to melt away but due to the lack of autopilot controls and the accumulated ice I had some difficulty with the controls in maintaining level flight. The Controller advised me that I was 400 FT below my assigned altitude and I corrected. The Controller gave me a STAR which took us to a lower MVA so that I could descend further. Seeing that I was in VMC and I could maintain visual clearance on the mountains; I canceled IFR and went direct to the airport. I had checked weather before my flight and while there were no tops' reports; the ceilings were lower which normally makes for lower tops. This ceiling was very thick. The reported freezing level was around 18;000 yet I began accumulated ice from 19;000 down to 16;000 FT. I had the altitude hold jack screw freeze up before two years ago and had my shop remove the old grease and replace [it] with new grease and yet it froze up again. Next time when I see forecast ceilings over the [mountains]; I will choose a different route of flight; either flying further north or further south. I plan to talk with my shop on why my autopilot ices up and if the grease they are using on the trim is the correct product for flying in cold weather. I can't say enough about the Controller and how well he took care of me in the icing conditions. I truly appreciate the assistance he gave me to get me out of the icing conditions and let me fly the plane.




Synopsis: A M20 elevator trim lubricant froze while in cruise flight at FL250 but a descent to 17;000 FT resulted in rime ice accumulation so further descent to 15;000 FT was made where the ice began to melt.