FAILED HSI; LACK OF RECENT EXPERIENCE; IMC CONDITIONS AND ICE ARE ALMOST MORE THAN PA23 PLT CAN HANDLE.

Narrative

WHILE BEING VECTORED FOR DEP FROM THE AREA; I NOTICED A DISCREPANCY IN HDG BTWN MY PRIMARY HSI AND MY BACK UP HDG INDICATOR (DG). I WAS ASSIGNED AN INITIAL HDG OF 050 DEGS; AND ON CLBOUT WAS INSTRUCTED TO TURN R HDG 180 DEGS. I INITIATED THE ASSIGNED R TURN NOTING THAT MY PRIMARY HDG INDICATOR; AN HSI; INDICATED A NORMAL TURN FROM A HDG OF 050 DEGS TO 090 DEGS WHERE IT FROZE IN PLACE. A XCHK OF MY STANDBY HDG INDICATOR AND TURN COORDINATOR INDICATED A TURN TO THE R; AND IT WAS BY REF TO MY BACK-UP DIRECTIONAL GYRO THAT I ROLLED WINGS-LEVEL ON MY ASSIGNED HDG. AT THIS POINT IN THE FLT THIS SHOULD HAVE BEEN A RELATIVELY INNOCUOUS INST FAILURE GIVEN THE EXISTENCE OF A STANDBY INST PERFORMING THE SAME FUNCTION A MERE 20 INCHES TO THE R. UNFORTUNATELY THIS WAS NOT TO BE THE CASE. REALIZING THAT MY PRIMARY HDG INDICATOR WAS NOT FUNCTIONING PROPERLY I DID WHAT MOST PLTS DO WITH AN INOP PIECE OF FLT INSTRUMENTATION: I TAPPED IT; THEN I TAPPED IT HARDER; THEN I TWISTED THE HDG INDICATOR AND CDI KNOBS IN A FUTILE ATTEMPT RESTORE FUNCTION. WITH MY ATTN THUS OCCUPIED; I CONTINUED MY CLB THROUGH MY ASSIGNED ALT OF 6000 FT AND WAS CLBING THROUGH 6500 FT WHEN ATC SUGGESTED THAT I 'CHK MODE C.' WHILE INITIATING AN ALT CORRECTION; I FOUND THAT THE ACFT WAS NOW IN AN UNCOMMANDED AND CERTAINLY UNINTENDED 30 DEG BANK TURN TO THE R. I ROLLED WINGS LEVEL ON A HDG OF APPROX 220 DEGS (40 DEGS R OF ASSIGNED HDG) AND FOUND IT NECESSARY HOLD CONSTANT L AILERON INPUT AND SUBSTANTIAL L RUDDER TO KEEP THE WINGS LEVEL. A QUICK SCAN OF THE ENG GAUGES REVEALED NO ANOMALIES WITH THE R ENG; NOR ANY PWR IMBAL. I NOW FOUND MYSELF TROUBLESHOOTING A DIRECTIONAL CTL PROB WITH AN INOP HDG INDICATOR; NO AUTOPLT (IT WAS COUPLED TO THE FAILED HSI); IN IMC; ICE; AND IN AN ACFT NOT YET CONFIGURED FOR CRUISE. THE LARGE PWR REDUCTION I MADE TO CORRECT FOR MY INITIAL ALT BUST WAS TEMPORARILY FORGOTTEN AS I WORKED AT KEEPING THE WINGS LEVEL; CONSEQUENTLY I DSNDED THROUGH MY ASSIGNED ALT BEFORE CORRECTING. AT THIS POINT I REALIZED THAT THE MINOR INST FAILURE WAS BECOMING A SERIOUS PROB AND I INFORMED ATC OF MY INTENTIONS TO DIVERT TO ZZZ FOR MECHANICAL REASONS AND SHOOT THE ILS. ATC PROVIDED PRIORITY HANDLING. IT SEEMED THAT THE ACFT REQUIRED AN INORDINATE AMOUNT OF L RUDDER TO MAINTAIN LEVEL FLT SO I TRIMMED THE ACFT ACCORDINGLY; NOTING THAT THE ACFT WOULD FLY 'TRUE' WHEN THE ACFT WAS TRIMMED WITH L RUDDER TRIM INDICATING HALF SCALE L OF NEUTRAL ON THE TRIM WHEEL INDICATOR. I FOUND THE SCAN NECESSARY TO EFFECTIVELY SHOOT THE APCH TO BE VERY AWKWARD: ATTITUDE INDICATOR IN FRONT OF ME; LOC/GS NEAR THE THROTTLE QUADRANT; AND DIRECTIONAL GYRO ON THE R SIDE OF THE COCKPIT. THIS WAS TEXT-BOOK 'INOP INST' FLYING AND IT WAS BY FAR MORE CHALLENGING IN ACTUAL CONDITIONS THAN IN TRAINING. I SET UP THE APCH IN NAV #2 A STANDARD VOR/LOC OBS BECAUSE I DIDN'T KNOW IF THE PRIMARY WOULD WORK IN THE FAILED HSI. CONSEQUENTLY; I FAILED TO GET A GS INDICATION UNTIL INSIDE THE FAF WHEN I REMEMBERED TO PUT THE LOC FREQ IN THE #1 NAV RADIO. IN THIS ACFT ALL GS INDICATIONS ARE SLAVED TO THE NAV #1 RADIO. I CONTINUED THE APCH TO SUCCESSFUL LNDG AT ZZZ EVEN THOUGH I HAD 2 FULL SCALE DEFLECTIONS OF THE LOC NEEDLE; ONE L; ONE R; I ACQUIRED THE RWY ABOUT 5 MI FROM THE THRESHOLD AND 1200 FT AGL AND WAS IN A POS TO MAKE A NORMAL LNDG. THIS INCIDENT IS THE RESULT OF A CHAIN OF EVENTS BEGINNING ON THE GND AT PREFLT; PERHAPS MONTHS EARLIER. 1) THE TWIN-ENG ACFT OPERATED BY MY COMPANY ARE UTILIZED ONLY IN 'BAD' WX OR FOR MANDATORY TRAINING; THEREFORE ANY FAILURE OF ANY INST OR SYS TENDS TO BE IN THE WORST POSSIBLE WX. THE LAST TIME THE INCIDENT ACFT HAD BEEN FLOWN WAS 8 MONTHS PREVIOUSLY (THE END OF LAST ICING SEASON). THIS IS NOT ENOUGH UTILIZATION TO KEEP OUR PLTS PROFICIENT IN THE ACFT; NOR TO ENSURE PROPER FUNCTIONING OF THE ACFT AND ITS SYS. 2) WHILE PREFLTING THE ACFT I SET BOTH THE ELEVATOR AND RUDDER TRIM TO THE NEUTRAL/TKOF POS. UNDOUBTEDLY THE RUDDER TRIM HAD BEEN PROPERLY SET TO 'FLT TRIM' BY THE LAST PERSONS TO FLY THE ACFT (8 MONTHS AGO); BUT 'FLT TRIM' WAS WAY L OF NEUTRAL. BY SETTING THE ACFT'S RUDDER TRIM TO NEUTRAL; I ACTUALLY RIGGED THE ACFT TO TURN R IN FLT; A CONDITION I DID NOT NOTE ON TKOF BECAUSE MY INITIAL HDG AND FIRST VECTOR WERE BOTH R TURNS. THIS CONDITION SHOULD HAVE BEEN SQUAWKED AND FIXED; AT THE VERY LEAST DISCOVERED IN VMC BEFORE FLT INTO 'HARD IFR.' 3) I WAS SLOW TO RESPOND TO THE UNFOLDING CIRCUMSTANCES; IN PART; DUE TO LACK OF FAMILIARITY AND PROFICIENCY IN THE ACFT. THE LAST TIME I FLEW A COMPANY AZTEC ON A SCHEDULED RTE WAS 7 MONTHS AGO (ALSO IN HARD IFR; ICE AND SNOW) THE KIND OF 'AUTOMATIC ACTION' AND COCKPIT FLOW DO NOT DEVELOP FLYING AN AIRPLANE 6 TIMES A YR.