PILOT AND RATED PAX ABOARD PA46 LOSE CONTROL OF THE AIRCRAFT WHILE DESCENDING IN LIGHT ICING CONDITIONS.

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I WAS PF AT 4000 FT ENRTE TO ZZZ. WE WERE ASSIGNED 4000 FT AS ATC WAS READY TO RADAR VECTOR US TO THE ILS LOCATED AT ZZZ. WE HAD DSNDED FROM AN ALT OF 16000 FT (WHERE WE WERE IN VFR CONDITIONS) TO IMC CONDITIONS. WE WERE IN IMC FOR APPROX 15 MINS. ALL ICING EQUIP WAS ON AND OPERATING. WE WERE PICKING UP LIGHT ICING AT THE TIME. (OUR PA46 IS APPROVED FOR FLT IN KNOWN ICING CONDITIONS.) I WAS ABOUT TO REQUEST A LOWER ALT (3000 FT) TO EXIT ICING CONDITIONS WHEN THE ACFT PITCHED UP 20 DEGS. MY HEADSET CAME OFF MY HEAD AS A RESULT OF THE JOLT. I IMMEDIATELY PITCHED FORWARD TO COMPENSATE/AVOID A STALL. I WAS ABLE TO LOWER THE ACFT TO A 5 DEG NOSE UP PITCH. I ALSO REDUCED THE MANIFOLD PRESSURE WHEN I WAS FINALLY ABLE TO LEVEL THE ACFT. ONCE I LEVELED; THE CTLS WERE UNRESPONSIVE. THE YOKE THEN PITCHED FORWARD DOWN TO APPROX 5 DEGS. I HAD DIFFICULTY PITCHING BACK TO LEVEL THE ACFT. I THEN ADVISED MY PNF I HAD NO CTL OF THE ACFT AND EXPERIENCING DIFFICULTY MAINTAINING LEVEL FLT. SHORTLY THEREAFTER; I REGAINED PARTIAL CTL RESPONSE AND BEGAN A DSCNT TO A LOWER ALT/WARMER AIR/VFR. THROUGHOUT; THE PNF WAS ATTEMPTING TO COMMUNICATE TO ATC. NOT HAVING FULL CTL EFFECTIVENESS; AND WITH TFC AROUND OUR POSITION; I REQUESTED THE PNF TO DECLARE AN EMER AND WE ARE DSNDING TO VFR IN AN ATTEMPT TO LAND AT THE NEAREST ARPT. ATC SUGGESTED ZZZ1 AND VECTORED US ON THE VOR APCH. AT APPROX 2500 FT MSL I REGAINED FULL CTL AUTH. THE FLT DIRECTOR; HOWEVER; WAS GIVING ERRONEOUS INDICATIONS. I SHUT IT OFF; ADVISED THE PNF TO CALIBRATE HIS DIRECTIONAL GYRO AND INITIALLY UTILIZED THE R SEAT INSTS UNTIL I FELT THE L SEAT INSTS WERE OPERATING PROPERLY WHICH I CONFIRMED SHORTLY THEREAFTER. AT THIS TIME I FELT COMFORTABLE THAT I HAD FULL CTL OF THE ACFT. BECAUSE I DID NOT KNOW WHAT HAD OCCURRED; I REQUESTED THE ILS TO ZZZ2; AS ZZZ1'S LONGEST RWY WAS UNDER 3000 FT (BELOW OUR COMFORT MARGIN FOR THIS ACFT). AT THIS TIME WE WERE IN/OUT OF IFR CONDITIONS. WE BROKE OUT AT 2000 FT MSL. WE LANDED UNEVENTFULLY AT ZZZ2. UPON INSPECTION; WE DISCOVERED NO ABNORMALITIES WITH THE CTL SURFACES. WHAT WE BELIEVE OCCURRED WAS WE PICKED UP ICE ON THE NON-PROTECTED SURFACE OF THE L OR R HORIZ STABILIZER AT THE GAP WHERE IT MEETS THE ELEVATOR. ICE MAY HAVE WEDGED ITSELF IN THIS GAP CAUSING CTL INEFFECTIVENESS. AS THE ICE MELTED; EFFECTIVENESS OF THE CTLS WAS REGAINED. NO ICE; HOWEVER; HAD REMAINED ON THE ACFT TO CORROBORATE THIS. THE FOLLOWING DAY WE FLEW THE ACFT BACK TO ZZZ (VFR) AND EXPERIENCED NO ANOMALIES.