Jet/Long Ranger/206
Flight Crew Multiengine; Flight Crew Commercial; Flight Crew Flight Instructor
Flight Crew Last 90 Days 25; Flight Crew Total 6000; Flight Crew Type 250
Communication Breakdown; Situational Awareness
Conflict NMAC
Flight Crew Took Evasive Action
Human Factors; Aircraft; Procedure
While returning from a patient drop off on a heading of 067 and 3500' a Cessna 172 passed just to the front of me and underneath me at less than 200' separation. Conditions were 5000 BKN; 10 M Vis with haze; wind 150@ 25kts.  I had just come from ZZZ and had been up with Approach.  Approach assigned me 3500' to get me above high speed jet traffic.  As this provided good visibility and more favorable winds I remained there until my decent.  The other aircraft was either not equipped with ADS-B or ADS-B Out may not be working correctly as I had no aircraft return or warnings visual or audio.  The first I saw him was through my chin bubble moving left to right; wings level in a slight climb.  I made several attempts to contact the aircraft on CTAF frequencies with no success. I immediately called [Dispatch] about the incursion. Upon landing I was provided the flight track and N number of the aircraft that passed underneath. I tracked it to a flight school in. I called the flight school and spoke to the instructor who confirmed he was in the aircraft performing maneuvers and had seen me on TCAS.  He claimed he had tried to avoid me but never saw me.  He told me his TCAS had me 200 ft above him.  At this point I ended the conversation and thanked him for his time.  Continuing this conversation beyond confirmation is not my responsibility. I know my systems were working very well because 10 min prior I had picked up high speed traffic flying [nearby] and was able to call it out to my crew.  I believe the flight school should address TCAS warnings and avoidance by more than 200 ft.  I have notified my [Chief Pilot]; I will submit safety reports as well.
B206L Captain reported NMAC while en route with radar services.