Narrative:

While being vectored for departure from the area; I noticed a discrepancy in heading between my primary HSI and my back up heading indicator (dg). I was assigned an initial heading of 050 degrees; and on climb out was instructed to turn right heading 180 degrees. I initiated the assigned right turn noting that my primary heading indicator; an HSI; indicated a normal turn from a heading of 050 degrees to 090 degrees where it froze in place. A xchk of my standby heading indicator and turn coordinator indicated a turn to the right; and it was by reference to my back-up directional gyro that I rolled wings-level on my assigned heading. At this point in the flight this should have been a relatively innocuous instrument failure given the existence of a standby instrument performing the same function a mere 20 inches to the right. Unfortunately this was not to be the case. Realizing that my primary heading indicator was not functioning properly I did what most pilots do with an inoperative piece of flight instrumentation: I tapped it; then I tapped it harder; then I twisted the heading indicator and CDI knobs in a futile attempt restore function. With my attention thus occupied; I continued my climb through my assigned altitude of 6000 ft and was climbing through 6500 ft when ATC suggested that I 'check mode C.' while initiating an altitude correction; I found that the aircraft was now in an uncommanded and certainly unintended 30 degree bank turn to the right. I rolled wings level on a heading of approximately 220 degrees (40 degrees right of assigned heading) and found it necessary hold constant left aileron input and substantial left rudder to keep the wings level. A quick scan of the engine gauges revealed no anomalies with the right engine; nor any power imbal. I now found myself troubleshooting a directional control problem with an inoperative heading indicator; no autoplt (it was coupled to the failed HSI); in IMC; ice; and in an aircraft not yet configured for cruise. The large power reduction I made to correct for my initial altitude bust was temporarily forgotten as I worked at keeping the wings level; consequently I descended through my assigned altitude before correcting. At this point I realized that the minor instrument failure was becoming a serious problem 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 aircraft required an inordinate amount of left rudder to maintain level flight so I trimmed the aircraft accordingly; noting that the aircraft would fly 'true' when the aircraft was trimmed with left rudder trim indicating half scale left of neutral on the trim wheel indicator. I found the scan necessary to effectively shoot the approach to be very awkward: attitude indicator in front of me; localizer/GS near the throttle quadrant; and directional gyro on the right side of the cockpit. This was text-book 'inoperative instrument' flying and it was by far more challenging in actual conditions than in training. I set up the approach in navigation #2 a standard VOR/localizer 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 localizer frequency in the #1 navigation radio. In this aircraft all GS indications are slaved to the navigation #1 radio. I continued the approach to successful landing at ZZZ even though I had 2 full scale deflections of the localizer needle; one left; one right; I acquired the runway about 5 mi from the threshold and 1200 ft AGL and was in a position to make a normal landing. This incident is the result of a chain of events beginning on the ground at preflight; perhaps months earlier. 1) the twin-engine aircraft operated by my company are utilized only in 'bad' WX or for mandatory training; therefore any failure of any instrument or system tends to be in the worst possible WX. The last time the incident aircraft had been flown was 8 months previously (the end of last icing season). This is not enough utilization to keep our pilots proficient in the aircraft; nor to ensure proper functioning of the aircraft and its system. 2) while preflting the aircraft I set both the elevator and rudder trim to the neutral/takeoff position. Undoubtedly the rudder trim had been properly set to 'flight trim' by the last persons to fly the aircraft (8 months ago); but 'flight trim' was way left of neutral. By setting the aircraft's rudder trim to neutral; I actually rigged the aircraft to turn right in flight; a condition I did not note on takeoff because my initial heading and first vector were both right turns. This condition should have been squawked and fixed; at the very least discovered in VMC before flight into 'hard IFR.' 3) I was slow to respond to the unfolding circumstances; in part; due to lack of familiarity and proficiency in the aircraft. The last time I flew a company aztec on a scheduled route 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.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.