ABLE FLT ASSIST BY APCH CTLR WHEN S76 ROTARY WINGED TFC DECLARES EMER DUE TO AN ACFT EQUIP PROB IN IFR FLT.

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ON AN IFR CLRNC; CLBING THROUGH 3200 FT; THE PLT'S SIDE HDG AND #2 ATTITUDE HDG REF SYS FAILURE INDICATIONS WERE DISPLAYED ON THE EHSI EFIS. REVERSION TO THE #1 HDG AND #1 ATTITUDE HDG REF SYS WERE ACCOMPLISHED. WITHIN APPROX 40-60 SECONDS; THE #1 HDG AND #1 ATTITUDE HDG REF SYS FAILED. THE PLT USING STANDBY COMPASS AND STANDBY ATTITUDE DIRECTION INDICATOR REQUESTED AN IMMEDIATE APCH INTO HPN DECLARING AN EMER SINCE ALL PRIMARY HDG SOURCES HAD FAILED. ATC EXPEDITED OUR APCH BUT WITH A STRONG XWIND IN HVY RAIN; IT TOOK QUITE A BIT OF CORRECTION TO FINALLY INTERCEPT THE LOC AND GS. WE LANDED WITHOUT FURTHER INCIDENT THANKS TO THE EXCELLENT HANDLING FROM ATC. THROUGH MUCH RESEARCH WITH OTHER SIKORSKY S76 OPERATORS WITH THE NEW LITEF AHRS OPTICAL GYROS; AND SIKORSKY ACFT REPRESENTATIVES; IT WAS DETERMINED THAT WE EXPERIENCED A MAGNETIC DISTURBANCE. IT IS MY HONEST OPINION THAT LITEF AND SIKORSKY WERE NEGLIGENT BY NOT INFORMING PLTS OR OPERATORS OF THIS POSSIBLE PROB OR HOW TO CORRECT IT. SINCE THIS INCIDENT; SIKORSKY HAS ISSUED A NEWLY APPROVED FLT MANUAL SUPPLEMENT ADDRESSING THIS OCCURRENCE AND A PLT CORRECTIVE ACTION TO FOLLOW.