CLE TRACON DEP CTLR TURNS ACR ON L PARALLEL RADAR VECTOR INTO OTHER ACR. SECOND ACR RPTED ACR TO HIS L IN SIGHT; BUT IS REQUIRED TO TAKE TCASII EVASIVE ACTION AS OTHER ACR TURNS INTO FLT PATH; DSNDING SLIGHTLY.

Narrative

TOOK OFF (X) BEHIND A COMPANY 30-SEAT TURBOPROP (Y) TOLD TO MAINTAIN VISUAL SEPARATION. ON THE CLBOUT; WE WERE BOTH GIVEN THE SAME VECTOR. INITIALLY THE OTHER ACFT WAS TO MY L AT ABOUT 10 O'CLOCK POS AT 700 FT HIGHER THAN I WAS AND PARALLEL COURSES (BOTH PLANES TCASII EQUIPPED). I TOLD MY FO TO LOWER THE NOSE AND DECREASE OUR CLB RATE TO KEEP THE OTHER ACFT ABOVE US. DEP CTLR ALSO TOLD ME TO MAINTAIN VISUAL SEPARATION WITH OTHER ACFT; THEN HE VECTORED OTHER PLANE TOWARDS ME. AND EVEN THOUGH OTHER PLANE WAS ABOVE US; THE AIRPLANE DSNDED TOWARDS US (POSSIBLY BASED ON HIS TCASII INFO BEING INACCURATE). WE GOT A TA ON OUR TCASII AT THIS POINT SO WE INCREASED OUR CLB RATE DRAMATICALLY. THE OTHER PLANE PASSED DIRECTLY UNDERNEATH US AT ABOUT 300-400 FT. ALTHOUGH I HAD THE OTHER ACFT IN SIGHT FROM TKOF UNTIL THE NEAR MISS; I COULDN'T ANTICIPATE AN ACFT; AT 10 O'CLOCK POS AND 700 FT ABOVE ME; TURNING TOWARDS ME AND DSNDING TOWARDS ME. PRIOR TO THE TURN TOWARDS ME; THE OTHER ACFT RPTED HAVING ME IN SIGHT.