POTENTIAL CONFLICT LTSS BTWN A BE02 IN CRUISE FLT AND A CLBING B767 FREIGHTER WHO CLBED ABOVE ASSIGNED ALT. BE02 FLC DID NOT CLB AWAY FROM ACFT Y; TCASI ON BOARD WITH TA CAPABILITY ONLY; FREIGHTER WITH NO TCAS AT ALL.

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WHILE ENRTE FROM SDF TO MKE; LEVEL AT FL220; OUR FLT EXPERIENCED A TCASI TA. EVENTS LEADING TO THE OCCURRENCE ARE DESCRIBED IN THE FOLLOWING PARAGRAPH. AT APPROX AM15 LCL; OUR FLT WAS IN CRUISE FLT AT FL220 WITH ALTIMETERS SET AT 29.92 WHEN ZID ADVISES US THAT A CARGO B767 IS NE OF OUR POS CLBING WBOUND TO FL210. NO TFC IS OBSERVED VISUALLY OR ON TCASI. FLT CONDITIONS AT THE TIME WERE IMC WITH AN ESTIMATED VISIBILITY OF 2 MI IN HAZE. NOTE THAT THE VISIBILITY IS ESTIMATED BASED ON HOW QUICKLY THE B767 DISAPPEARED ONCE IT WAS ACQUIRED VISUALLY. SHORTLY AFTER ATC ADVISES OF THE TFC; OUR TCASI ISSUES A TA. THE B767 TARGET APPEARS ON THE DISPLAY AT -2700 FT AND CLBING WITH AN ESTIMATED RANGE OF 3 MI. THE FO QUICKLY ADVISES ATC OF OUR TA AND QUERIES ATC TO VERIFY THAT THE B767 IS LEVELING AT FL210. SIMULTANEOUSLY; I MONITOR THE RATE OF CLB AND DISTANCE OF THE TARGET AND ATTEMPT TO VISUALLY ACQUIRE THE TARGET. ATC QUERIES THE B767 CREW IF THEY ARE LEVELING AT FL210 AND THEY REPLY THAT THEY ARE. AT THIS POINT THE TCASI ISSUES A SECOND ADVISORY WITH THE TARGET PASSING THROUGH -1000 FT AND CLBING WITH TARGETS NEARLY MERGED. THE RATE OF VERT CLOSURE IS REDUCED AT THIS TIME. NOTHING IS VISIBLE OUTSIDE OF THE ACFT UNTIL THE B767 EMERGES AT THE 10 O'CLOCK POS DOWN LOW AND 'CLOSE.' I POINT OUT TO THE FO THAT I HAVE THE TFC IN FRONT OF THE L WING. AT THIS TIME; THE FO IS TALKING WITH ATC AND TELLS THEM WE HAVE THE TFC 'IN CLOSE.' MY ESTIMATION OF HORIZ SEPARATION IS LESS THAN 1 MI; WITH VERT SEPARATION NOTED ON TCASI TO BE -700 FT. ACTUAL VERT SEPARATION MAY NOT HAVE BEEN OBSERVED BECAUSE MY FOCUS WAS OUTSIDE OF THE ACFT AT THIS TIME. AFTER ATC PASSED THE B767 TO THE NEXT SECTOR; ATC INDICATED TO US THAT THEY DID SHOW THE B767 ABOVE THEIR ASSIGNED ALT AND THEY WOULD BE REQUIRED TO FILE A RPT REGARDING OUR TA. THEY ALSO INQUIRED WHETHER WE HAD ANY COMMENT. MY COMMENTS WERE DIRECTED TO WHAT WE OBSERVED OUTSIDE OF THE ACFT AND WHAT WAS OBSERVED ON THE TCASI. ADDITIONAL INQUIRIES WERE MADE BY ME TO VERIFY THAT ATC SHOWED US CONTINUOUSLY AT FL220; AS WELL AS LOCATION OF THE INCIDENT. NO DEV FROM FL220 WAS OBSERVED BY ATC. THE REST OF THE FLT TO MKE WAS UNEVENTFUL BUT INWARDLY REFLECTIVE.