HELI Y HAD NMAC LTSS FROM ACR X IN ARSA ATA. SYS ERROR SEE AND AVOID CONCEPT.

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I WAS ON AN EMS FLT ENRTE FROM THE TOWN OF XYZ TO HOSPITAL A IN ZZZ. THIS RTE PASSES THROUGH THE ZZZ ARSA W OF THE ARPT. AS I APCHED THE ARPT THE CTLR ADVISED ME OF AN ACFT DEPARTING RWY 24R PROCEEDING W. THIS ACFT WAS CLBING AND THE CTLR WARNED ME OF WAKE TURB. I ALTERED MY COURSE ABOUT 10 DEGS L TO FLY ABOVE THE WAKE TURB. AS I BECAME ABOUT A MI W OF THE ARPT THE CTLR STATED THAT HE THOUGHT AN ACFT WAS TAKING OFF. I LOOKED TOWARD THE ARPT AND SAW AN ACFT ROLLING ON RWY 24R. I STATED TO ATC THAT I WOULD FLY TOWARD THE CTR OF THE ARPT WHEN I SAW A LARGE ACR X ABOUT 300 FT AWAY. IT WAS OBSCURED BY MY INST PANEL AND WAS VISIBLE ONLY FOR AN INSTANT. HE WAS BANKING HARD R AND WAS PROBABLY STILL ON THE TWR FREQ. SINCE MY HELI IS FLOWN FROM THE R SEAT AND THE OTHER ACFT WAS INITIALLY TO MY FRONT L LOWER; I COULD NOT SEE HIM. THERE WERE MANY CARGO AND AIRLINE ACFT DEPARTING. I PROBABLY SHOULD HAVE BEEN SWITCHED TO THE TWR FREQ OR BEEN ASKED TO FLY OVER THE CTR OF THE ARPT. SUPPLEMENTAL INFORMATION FROM ACN 242792: RADAR POINTED OUT OVER FLT VFR HELI Y. I CLRED ACR X FOR TKOF HAVING HELI Y IN SIGHT. AS ACR X WAS TURNING; I POINTED OUT HELI Y. ACR X SAID TFC IN SIGHT; SO I SWITCHED ACR X TO DEP CTL. (I FAILED TO TELL ACR X TO MAINTAIN VISUAL SEPARATION.) CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: RPTR STATES THAT A PATIENT WAS ON BOARD BUT THIS DID NOT INFLUENCE ANY OUTCOME OF INCIDENT.