Narrative:

On our last circuit in the pattern, we were transitioning to approach speed when we both looked to the upper right of the airplane (approximately 2 O'clock position) and saw a single engine small aircraft Y approximately 100' above our altitude. Within about 3 seconds, both of us in the airplane saw the small aircraft Y and tower called traffic 'right in front of you.' tower controller said that he did not have an unusual primary target. Apparently he noticed the small aircraft Y first by sight. When we in the airplane saw the traffic we expected an immediate right turning descent to avoid further conflict. The tower established communication with the small aircraft Y. The small aircraft Y could receive but not transmit. Tower dubbed him. 'No radio small aircraft Y' for communication. I landed with no further incident and the small aircraft Y followed us in. The small aircraft Y obviously did not see us, though our color is daytona orange. There are many uncontrolled fields the small aircraft Y could have chosen. As fare as his altitude is concerned, with no transmitting capability, the small aircraft Y could not have requested the local barometric pressure. We were approximately 100' above traffic pattern altitude. If he came into a situation conducive to the altimeter showing higher than his actual altitude, he could have indicated a very different altitude, one he presumed would set him above the greenville downtown traffic pattern altitude.

Related reports:

Google
 

Original NASA ASRS Text

Title: NMAC BETWEEN GA SMA IN TRAFFIC PATTERN AND NORAC GA SMA ENTERING ATA.

Narrative: ON OUR LAST CIRCUIT IN THE PATTERN, WE WERE TRANSITIONING TO APCH SPD WHEN WE BOTH LOOKED TO THE UPPER RIGHT OF THE AIRPLANE (APPROX 2 O'CLOCK POS) AND SAW A SINGLE ENG SMA Y APPROX 100' ABOVE OUR ALT. WITHIN ABOUT 3 SECS, BOTH OF US IN THE AIRPLANE SAW THE SMA Y AND TWR CALLED TFC 'RIGHT IN FRONT OF YOU.' TWR CTLR SAID THAT HE DID NOT HAVE AN UNUSUAL PRIMARY TARGET. APPARENTLY HE NOTICED THE SMA Y FIRST BY SIGHT. WHEN WE IN THE AIRPLANE SAW THE TFC WE EXPECTED AN IMMEDIATE RIGHT TURNING DSCNT TO AVOID FURTHER CONFLICT. THE TWR ESTABLISHED COM WITH THE SMA Y. THE SMA Y COULD RECEIVE BUT NOT XMIT. TWR DUBBED HIM. 'NO RADIO SMA Y' FOR COM. I LANDED WITH NO FURTHER INCIDENT AND THE SMA Y FOLLOWED US IN. THE SMA Y OBVIOUSLY DID NOT SEE US, THOUGH OUR COLOR IS DAYTONA ORANGE. THERE ARE MANY UNCONTROLLED FIELDS THE SMA Y COULD HAVE CHOSEN. AS FARE AS HIS ALT IS CONCERNED, WITH NO XMITTING CAPABILITY, THE SMA Y COULD NOT HAVE REQUESTED THE LCL BAROMETRIC PRESSURE. WE WERE APPROX 100' ABOVE TFC PATTERN ALT. IF HE CAME INTO A SITUATION CONDUCIVE TO THE ALTIMETER SHOWING HIGHER THAN HIS ACTUAL ALT, HE COULD HAVE INDICATED A VERY DIFFERENT ALT, ONE HE PRESUMED WOULD SET HIM ABOVE THE GREENVILLE DOWNTOWN TFC PATTERN ALT.

Data retrieved from NASA's ASRS site as of August 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.