MLG RECEIVED A TCASII RA WHILE ON FINAL APCH.

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I WAS FLYING A VFR HELI OUT OF THE ORD TCA ON THE TAFTS #1 HELI RTE. I WAS APPROX 2 MI E OF THE FIELD WHEN ORD S TWR CLRED AN ACR MLG TO LAND RWY 27L AND TO BE ADVISED THAT A VFR HELI WAS LOW LEVEL; N OF COURSE; EBOUND. AT THAT MOMENT; THE ACR PLT PROCEEDED TO TELL ORD HE THOUGHT THIS WAS UNSAFE. HIS MAIN REASON WAS HE HAD A TCASII ALERT WITH AN RA INDICATION. THE TWR THEN SAID TO ACR 'WHAT WOULD YOU LIKE TO DO. I HAVE BOTH OF YOU IN SIGHT. IT'S VFR. DO YOU WANT TO LAND OR GAR.' THE ACR PLT STATED HE WANTED TO LAND AND PROCEEDED TO DO SO. I EXITED THE TCA TO THE E. I BELIEVE TO IMPROVE THE HANDLING AND UNDERSTANDING BTWN VFR HELIS AND IFR AIRPLANES IN THESE MAJOR TERMINALS REQUIRES THAT THE VFR HELI RTE CHARTS BE MADE AND ADDED TO INST APCH CHARTS. IN THE CASE OF CHICAGO IT SHOULD BE INSERTED BEFORE THE BRADFORD 2 ARR (BDF.BDF2) STAR SHOWING THE HELI RTES INTO AND OUT OF THE TCA. ALSO; A NOTE SHOULD BE ON IT STATING TO TCASII EQUIPPED ACFT; 'BE AWARE OF LOW FLYING HELIS IN THE TCA IN VFR AND LESS THAN VFR WX.' HOPEFULLY; THIS MAY HELP; SINCE THE ACR PLT MADE NO EFFORT TO CONFIRM THE RA VISUALLY.