Beechcraft Twin Piston Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 20; Flight Crew Total 4042; Flight Crew Type 1358
Aircraft Equipment Problem Critical; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Flight Crew Overcame Equipment Problem; Flight Crew Took Evasive Action
Aircraft
While turning onto the final approach course for RNAV/GPS Approach to RW26; my HSI (both Heading Indicator and CDI) began to fail; acting erratically.  While still outside of the FAF; the HSI began to spin wildly out of control; also causing my MFD to continually change its display and course information; both of which were quite distracting. I had just entered IMC in a snow squall.  While reported conditions at the airport were VFR; I was over the mountains to the east of PSF and in solid IMC.  I elected to discontinue the approach.  I turned 180 degrees first to the north and then to the east to return to good VFR conditions that I had just left.  I did this rather than risk continuing the approach; or remain in IMC to execute the published Missed Approach; not being able to fly an exact heading.  Radar services had been terminated by Albany approach; and when I was able to re-establish contract I informed them of the situation and asked for clearance to a higher altitude on a southeast heading; which they provided.  I did not declare an emergency which perhaps I should have as I did not conform to the Missed Approach Procedure.  There were no conflicts.
Beech B55 pilot reported HSI failure in IMC on approach to PSF.