Narrative:

A B757 inbound to cle was at 7000 ft and I issued a turn to the downwind leg for runway 23L. As the aircraft started his turn I noticed another beacon slash untracked converging with my traffic. The untracked aircraft was at 7000 ft also. I took evasive action giving the B757 an immediate left turn and a descent to 6000 ft. Once the B757 started turning the traffic disappeared off the scope. Another controller got the beacon code which was the same as my B757's beacon code. I then realized that the intruding aircraft was really the false target or ring around from my B757. This occurs many times a day, however, the false target does not usually appear in conflict with real traffic.

Google
 

Original NASA ASRS Text

Title: CTLR AT CLE TRACON RPTS A FALSE BEACON TARGET WAS TAKEN FOR TFC AND HE DSNDED HIS ACFT FOR SEPARATION. THE UNTRACKED TARGET DISPLAYED ALT AND THE SAME BEACON CODE AS HIS ACFT.

Narrative: A B757 INBOUND TO CLE WAS AT 7000 FT AND I ISSUED A TURN TO THE DOWNWIND LEG FOR RWY 23L. AS THE ACFT STARTED HIS TURN I NOTICED ANOTHER BEACON SLASH UNTRACKED CONVERGING WITH MY TFC. THE UNTRACKED ACFT WAS AT 7000 FT ALSO. I TOOK EVASIVE ACTION GIVING THE B757 AN IMMEDIATE L TURN AND A DSCNT TO 6000 FT. ONCE THE B757 STARTED TURNING THE TFC DISAPPEARED OFF THE SCOPE. ANOTHER CTLR GOT THE BEACON CODE WHICH WAS THE SAME AS MY B757'S BEACON CODE. I THEN REALIZED THAT THE INTRUDING ACFT WAS REALLY THE FALSE TARGET OR RING AROUND FROM MY B757. THIS OCCURS MANY TIMES A DAY, HOWEVER, THE FALSE TARGET DOES NOT USUALLY APPEAR IN CONFLICT WITH REAL TFC.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.