Narrative:

Aircraft Y (C172) called inbound 8 mi southwest of airport for full stop. Aircraft X (C402) called 10 mi west of airport for full stop. Aircraft Y was actually 8 mi directly west of airport. I observed a primary target approaching from the southwest. Using position correlation, I assumed the primary target southwest was aircraft Y and advised him his transponder appeared inoperative. At 5 mi west of the airport, the transponder mode C for aircraft Y appeared on the d-brite, although I still could not see the aircraft with or without binoculars. Aircraft X was less than 2 mi behind aircraft Y and was indicating 170 KTS while aircraft Y was indicating 80 KTS. I instructed aircraft X to make a left 360 degree turn to avert a conflict. The radar coverage problem and the erroneous position report of aircraft Y were the causes of this conflict. As for the primary target I observed to the southwest, it disappeared from the d-brite at about the same time that the secondary target for aircraft Y appeared directly west of the airport. Perhaps the primary target was actually a ghost target.

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Original NASA ASRS Text

Title: ATCT LCL CTLR BELIEVES TMB APCH RADAR HAS A BLIND SPOT W AND SW OF THE ARPT.

Narrative: ACFT Y (C172) CALLED INBOUND 8 MI SW OF ARPT FOR FULL STOP. ACFT X (C402) CALLED 10 MI W OF ARPT FOR FULL STOP. ACFT Y WAS ACTUALLY 8 MI DIRECTLY W OF ARPT. I OBSERVED A PRIMARY TARGET APCHING FROM THE SW. USING POS CORRELATION, I ASSUMED THE PRIMARY TARGET SW WAS ACFT Y AND ADVISED HIM HIS XPONDER APPEARED INOP. AT 5 MI W OF THE ARPT, THE XPONDER MODE C FOR ACFT Y APPEARED ON THE D-BRITE, ALTHOUGH I STILL COULD NOT SEE THE ACFT WITH OR WITHOUT BINOCULARS. ACFT X WAS LESS THAN 2 MI BEHIND ACFT Y AND WAS INDICATING 170 KTS WHILE ACFT Y WAS INDICATING 80 KTS. I INSTRUCTED ACFT X TO MAKE A L 360 DEG TURN TO AVERT A CONFLICT. THE RADAR COVERAGE PROB AND THE ERRONEOUS POS RPT OF ACFT Y WERE THE CAUSES OF THIS CONFLICT. AS FOR THE PRIMARY TARGET I OBSERVED TO THE SW, IT DISAPPEARED FROM THE D-BRITE AT ABOUT THE SAME TIME THAT THE SECONDARY TARGET FOR ACFT Y APPEARED DIRECTLY W OF THE ARPT. PERHAPS THE PRIMARY TARGET WAS ACTUALLY A GHOST TARGET.

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.