FLC OF AN ATR42 OBSERVED A BEECH 35 AT THEIR SAME ALT AND GOING IN THE OPPOSITE DIRECTION WITH NO TIME TO TAKE EVASIVE ACTION DURING DEP CLB AND JUST GETTING READY TO BE TURNED OVER TO CTR FROM DEP CTL. THE BE35 WAS NOT AT THE APPROPRIATE ALT FOR THE DIRECTION OF FLT.

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OUR FAR PART 121 FLT DEPARTED CMH AND WAS BEING VECTORED BY DEP PRIOR TO BEING TURNED ON COURSE. OUR HDG WAS 270 DEGS AND THE CAPT WAS THE PF THIS LEG BACK TO ORD. OUR TKOF AND CLB HAD BEEN ROUTINE TO THIS POINT. UPON PASSING 8500 FT MSL; BOTH THE CAPT AND MYSELF SPOTTED A V-TAIL BONANZA AT OUR 12:30 O'CLOCK POS GOING THE OPPOSITE DIRECTION. OUR 2 ACFT CAME WITHIN ABOUT 1000 FT OF EACH OTHER. BOTH CMH DEP AND ZID SAID THEY DID NOT SHOW ANY OTHER ACFT IN OUR AREA WHEN WE LATER TOLD THEM WHAT HAD JUST OCCURRED. CONTRIBUTING FACTORS WERE: 1) THE V-TAIL WAS CRUISING AT 8500 FT ON A 090 DEG HDG. THIS WAS THE WRONG ALT FOR DIRECTION OF FLT. 2) THE BONANZA DID NOT HAVE HIS XPONDER ON; SO WE DID NOT GET ANY TCASII INFO ON HIM. THIS ALSO KEPT CMH AND IND FROM PICKING HIM UP ON RADAR. 3) THE BONANZA WAS EXTREMELY CLOSE TO THE CLASS C AT CMH TO NOT BE IN RADIO COMS WITH THEM. 4) ALTHOUGH BOTH OF US WERE SCANNING FOR TFC; THIS V-TAIL BECAME A REAL THREAT TO OUR FLT. WE DON'T THINK HE EVER SAW US BECAUSE HE NEVER ALTERED HIS COURSE IN ANY WAY.