PLT OF AN ATX TWIN MADE A MISSED APCH AND TURNED BACK TO VFR CONDITIONS AFTER LOSING PWR ON 1 ENG DUE TO ICE AND NOTICING THE EFFECTS OF ICE ON THE ACFT. HOWEVER; HE FAILED TO NOTIFY ATC OF HIS ABANDONMENT OF HIS APCH AND CHANGE IN DIRECTION OR EMER STATUS.

Narrative

ON THE NIGHT OF FEB/XX/96; I WAS PIC ON A SCHEDULED FREIGHT RUN INTO HELENA; MT. THE WX AT HLN WAS FAIRLY DECENT; 1500 FT OVCST; 7 MI AND SNOW. THERE WAS A FRONT PASSING THROUGH AND FLT SVC CALLED FOR OCCASIONAL LIGHT TO MODERATE ICING FROM THE SURFACE TO 16000 FT. ZLC HANDED ME OFF TO HLN APCH. I WAS CLRED TO HAUSER NDB VIA THE 15 MI ARC AT 13000 FT. AS I STARTED TO INTERCEPT THE ARC; I WAS CLRED FOR THE ILS RWY 27 APCH AT HLN. AT THIS POINT; ICE BEGAN TO BUILD ON THE ACFT AT AN ALARMING RATE TO THE POINT THAT I WAS HAVING TO MAINTAIN CRUISE PWR TO HOLD THE GS. I WAS ALSO EXPERIENCING THE WORST ST ELMO'S FIRE I HAVE EVER SEEN. THE L ENG ENCOUNTERED INDUCTION ICING AND BEGAN TO QUIT; ALSO THE GS BEGAN TO BECOME INTERMITTENT AND FLAG. I HAD TRIED TO BOOT THE ICE OFF THE WINGS BUT TO NO AVAIL. I DECIDED TO BREAK OFF THE APCH AND INTERCEPT VICTOR 247 WHICH I HAD BEEN ON BEFORE RECEIVING APCH CLRNC BECAUSE I KNOW THE RTE WAS VFR TO THE E 20 DME. IT WAS SOMETIME DURING THE INTERCEPT TO VICTOR 247 THAT I MANAGED TO GET THE L ENG BACK TO FULL PWR BY PULLING THE ALTERNATE AIR DOOR. I WAS TALKING TO APCH ALL OF THE WAY BUT THERE WAS SOME MISUNDERSTANDING ABOUT ALT AND POS; I ALSO FAILED TO DECLARE AN EMER WHICH I SHOULD HAVE. I WAS NOT THE ONLY ONE TO HAVE PROBS. 2 OTHER ACFT DECLARED EMERS. I FEEL I MADE THE BEST POSSIBLE DECISION BY TURNING AROUND AND LEAVING THE AREA. THE ILS RWY 27 APCH INTO HLN IS WELL KNOWN FOR POCKETS OF SEVERE ICING. WITH THE STATIC ELECTRICITY AFFECTING THE NAV RADIOS; I HAD BEGUN TO DOUBT MY SITUATIONAL AWARENESS. THE L ENG WAS PROBABLY ONLY MAKING 35-40 PERCENT PWR; AND I FELT WITH THE MODERATE TO SEVERE TURB INVOLVED WITH THE PASSAGE OF THIS FRONT; CONTINUATION OF THE APCH WOULD PRODUCE DISASTROUS RESULTS. I FEEL THIS SIT WAS CAUSED BY UNFORECAST SEVERE ICING CONDITIONS AND MAY NOT HAVE BEEN PREVENTED BUT THE DANGER WAS INTENSIFIED BY HLN NOT HAVING RADAR. IF RADAR WOULD HAVE BEEN IN PLACE AT HLN THERE WOULD NOT HAVE BEEN A DOUBT TO THE CTLRS OF MY POS AT ANY TIME. I ALSO FAILED TO DECLARE AN EMER; WHICH SHOULD HAVE BEEN THE FIRST THING THAT HAPPENED BEFORE I DEVIATED BACK TO VFR CONDITIONS. IN MY MIND; I MADE THE RIGHT MOVES BECAUSE I HAD BEGAN TO DOUBT MYSELF AND EQUIP. HLN IS SURROUNDED BY MOUNTAINOUS TERRAIN AND IS NOT A PLACE TO DOUBT ONE'S EQUIP. I SHOULD HAVE BEEN IN BETTER CONTACT WITH ATC. I WAS OVERLOADED WITH EMERS AND TOO BUSY TO LET ATC KNOW I WAS IN TROUBLE.