A HELI PLT; WHILE ON AN 'EMER MEDICAL SVC' MISSION; ENTERED 'IMC' WITH NO IFR FLT PLAN.

Narrative

WE HAD FLOWN 52 MINS TO A MINE AND BEEN ON SCENE FOR 23 MINS BEFORE THE START OF THIS LEG. WE (MYSELF; 1 NURSE AND 1 PARAMEDIC) HAD PICKED UP A PATIENT AND WERE ENRTE TO THE HOSPITAL. ABOUT 2 MINS AFTER TKOF; I CROSSED A RIDGE AT APPROX 300 FT AGL AND 60 KTS ON A WESTERLY HEADING. AS THE GND DROPPED STEEPLY AWAY; I LOST VISUAL CONTACT WITH THE GND. THE COMBINATION OF A LIGHT SNOW FALLING; SNOW COVERED TERRAIN AND LOW ILLUMINATION PRODUCED A 'WHITEOUT' SIT IN WHICH I HAD NO VISIBLE HORIZON AND NO VISUAL CONTACT WITH THE SURFACE. I FELT THAT MY ONLY CHOICE WAS TO COMMIT TO AN INADVERTENT IMC PLAN. I CHOSE THIS OPTION BASED ON MY TRAINING AND EXPERIENCE. (I CURRENTLY FLY HELICOPTERS AND ROUTINELY PRACTICE INADVERTENT IMC AS WELL AS IFR FLT.) I ALREADY HAD A GPS COURSE PLOTTED DIRECT TO THE HOSPITAL. I LEVELED THE ACFT; APPLIED CLB PWR AND CLBED ON COURSE. I TUNED 121.5 AND CALLED FOR ANY STATION. AN ACR X ACKNOWLEDGED. I INFORMED THEM THAT I WAS INADVERTENT IMC AND ASKED FOR THE CTR FREQ FOR THAT AREA. THEY CALLED BACK WITH THE FREQ; WHICH I TUNED AND CONTACTED CTR. CTR PROVIDED ME WITH A SQUAWK; IDENTED ME AND PROVIDED A VECTOR. DURING THIS TIME; I HAD THE MEDICAL CREW PROVIDE ME WITH OXYGEN VIA A NASAL CANNULA AT 15 LITERS PER MIN TO HELP PREVENT HYPOXIA. I ALSO CONTINUED MY CLB TO 12500 FT MSL; KNOWING THAT I WOULD REMAIN CLR OF LCL TERRAIN AT THIS ALT. AFTER CHKING WX AT DEST (3800 FT OVCST I THINK) AND ZZZ (8000 FT BROKEN); I ELECTED TO GO TO ZZZ. THE CTR PROVIDED A VECTOR TO ZZZ AND I SET ZZZ ARPT IN THE GPS NAV. THE FLT PROCEEDED NORMALLY WITH CTR LETTING ME DOWN TO 11000 FT MSL ABOUT 30 MI FROM ZZZ. AT ABOUT 15 MI W OF ZZZ; I ENCOUNTERED VFR CONDITIONS; INFORMED CTR; AND BEGAN MY DSCNT. I ESTIMATE THAT I SPENT ABOUT 35 MINS ABOVE 10000 FT. WE CONTINUED TO THE HOSPITAL AND DROPPED OUR PATIENT AS NORMAL. I DEPARTED THE HOSPITAL AND LANDED AT ZZZ ARPT WITH ABOUT 1 HR AND 10 MINS OF FUEL ONBOARD. THE WX ENRTE TO THE SCENE STARTED WITH AT LEAST 8000 FT MSL CEILINGS AND NO SNOW. WE ENCOUNTERED SNOW AND LOWERING CEILINGS ABOUT 20 MI SE OF THE MINE. VISIBILITY DROPPED TO 3-4 MI AND APPROX 2000 FT AGL CEILINGS AS WE APCHED THE MINE.