GSP CTLR CONCERNED WITH RECURRING ERRONEOUS ARTS IIE; MODE C ALERTS.

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THE RADAR BEACON SYS AND/OR ARTS AT GSP HAS HAD CHRONIC PROBS IN REGARDS TO MODE C ALT RPTING FOR MANY YRS. QUITE OFTEN; WHEN TWO ACFT PASS CLOSE LATERALLY; REGARDLESS OF ALT; THE MODE C OF ONE OR BOTH ACFT DISPLAYS ERRONEOUS DATA FOR SEVERAL SWEEPS OF THE RADAR. THIS CAN LEAD TO THE CONFLICT ALERT SOUNDING EVEN THOUGH THE ACFT ARE NOT IN CONFLICT. IT IS VERY DISCONCERTING; AS A CTLR; TO HEAR A CONFLICT ALERT; THEN LOOK AND SEE TWO IFR ACFT LESS THAN A MI APART INDICATING THE SAME ALT EVEN THOUGH THEY ARE ACTUALLY SEPERATED BY SEVERAL THOUSAND FT. IT IS ALSO MY UNDERSTANDING THAT GSP IS NOT THE ONLY ATC FAC AFFECTED BY THIS PROB. THIS PROB EXISTED PRIOR TO THE IMPLEMENTATION OF ARTS IIE BUT MORE NOTICE IS BROUGHT TO IT NOW BECAUSE OF THE MODE C INTRUDER ALERT NOT PREVIOUSLY AVAILABLE UNDER ARTS IIA. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT A FAC SPECIALIST AND THE FAA TECHNICAL CENTER ARE LOOKING INTO THIS PROB. THE RPTR ADVISED OF A RECENT OCCURRENCE THAT FURTHER IDENTIFIES THE PROB. GSP WAS WORKING AN ENROUTE ACFT AT 9;000 FT AND ZTL WAS WORKING AN ENROUTE ACFT DESCENDING FROM FL350 TO FL310. WHEN FLT PATHS CROSSED; THE ARTS INITIATED A CONFLICT ALERT DISPLAYING BOTH ACFT AT 31;150 FT. THE RPTR ALLEGES THAT RPTS RECEIVED FROM THE FAA TECH CENTER ACKNOWLEDGE THAT THERE IS A PROB; BUT HAVE NOT PROVIDED SOFTWARE PATCH CORRECTIONS.