INADVERTENT IMC IN VFR FLT BY A B-06 EMS HELI WHEN ENCOUNTERING FORESTRY GENERATED SMOKE FROM A CTLED BURN NEAR ZZZ; US.

Narrative

THE FLT WAS A VFR FLT ENRTE TO ZZZ FOR REFUEL FOR AN EMS HOSPITAL XFER FROM ZZZ1. AFTER TAKING OFF FROM ZZZ2; WE WERE DIVERTED BY OUR DISPATCH TO ZZZ. OUR ACFT ONLY HAS DUAL GPS AND RATED FOR VFR FLT ONLY. WX RPTED UNLIMITED CEILINGS AND VISIBILITY. ENRTE; WE ENCOUNTERED SMOKE FROM A CTLED BURN BY THE FORESTRY SVC. THE SMOKE WAS MOVING HORIZ AND VISIBILITY WAS STILL ACCEPTABLE FOR VFR CONDITIONS. AS THE VISIBILITY DECREASED; I FELT I COULD CLB OVER THE SMOKE SEEING BLUE SKIES ABOVE. WHEN I REALIZED THAT I WAS NOT GOING TO GET OVER THE TOP; I REALIZED THAT VISIBILITY WAS DECREASING RAPIDLY. INSTEAD OF TRYING TO TURN AROUND; I LEVELED OFF AND MAINTAINED 4000 FT MSL AND REMAINED ON COURSE. I THEN CALLED APCH ON #2 VHF FREQ AND DECLARED 'INADVERTENT IMC.' THEY TOLD ME TO REMAIN VMC AND CHK ATIS. AFTER I TOLD THEM I LOST VMC; THEY THEN GAVE A SQUAWK CODE AND ALT AND CONTINUE DIRECT COURSE TO ZZZ. AFTER APPROX 5-10 MI; I REGAINED VMC; CANCELED IFR; AND LANDED AT ZZZ WITH NO FURTHER ENCOUNTER WITH SMOKE.