Narrative:

The radar beacon system and/or ARTS at gsp has had chronic problems in regards to mode C altitude reporting for many yrs. Quite often, when two aircraft pass close laterally, regardless of altitude, the mode C of one or both aircraft displays erroneous data for several sweeps of the radar. This can lead to the conflict alert sounding even though the aircraft are not in conflict. It is very disconcerting, as a controller, to hear a conflict alert, then look and see two IFR aircraft less than a mi apart indicating the same altitude even though they are actually seperated by several thousand ft. It is also my understanding that gsp is not the only ATC facility affected by this problem. This problem 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 reporter revealed the following information: reporter states that a facility specialist and the FAA technical center are looking into this problem. The reporter advised of a recent occurrence that further identifies the problem. Gsp was working an enroute aircraft at 9,000 ft and ZTL was working an enroute aircraft descending from FL350 to FL310. When flight paths crossed, the ARTS initiated a conflict alert displaying both aircraft at 31,150 ft. The reporter alleges that reports received from the FAA tech center acknowledge that there is a problem, but have not provided software patch corrections.

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Original NASA ASRS Text

Title: GSP CTLR CONCERNED WITH RECURRING ERRONEOUS ARTS IIE, MODE C ALERTS.

Narrative: 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.

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.