Narrative:

Tmb is a VFR tower with a BRITE radar display that feeds off of mia approach radar. Due to a newly erected building, we have developed a blind spot west of the field on the BRITE display. I was working local control north. A P28B was on final runway 9L, with a small helicopter in trail approaching the field from the west. I had not yet visually idented the P28B. I was resolving potential conflicts to the east, as well as coordinating turning an aircraft through the local control south controller's airspace when C172 called for departure from runway 9L. I looked at the BRITE display and saw a primary target on a 2 mi final for runway 9L and assumed it was the P28B. I knew the helicopter was flying at or below 500 ft. Due to line-of-sight limitations, helicopters at low level oftentimes do not show up on radar. I attributed the lack of a second target to this fact. I told the C172 to taxi into position and hold (traffic was clearing downfield). Fortunately, the ground controller was alert and pointed out that the P28B was on 1/2 mi final. Just as I keyed my microphone to send the P28B around, the pilot initiated a go around himself. Adequate separation was maintained. In hindsight, the primary target I observed north the BRITE display was the helicopter, and the P28B was not showing up at all. The blind spot has been reported to the appropriate personnel, and solutions are being considered.

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Original NASA ASRS Text

Title: PA28, ON SHORT FINAL RWY 9L AT TMB, EXECUTES GAR DUE TO TFC ON RWY AS THE GND CTLR ADVISES THE LCL CTLR OF THE POTENTIAL CONFLICT.

Narrative: TMB IS A VFR TWR WITH A BRITE RADAR DISPLAY THAT FEEDS OFF OF MIA APCH RADAR. DUE TO A NEWLY ERECTED BUILDING, WE HAVE DEVELOPED A BLIND SPOT W OF THE FIELD ON THE BRITE DISPLAY. I WAS WORKING LCL CTL N. A P28B WAS ON FINAL RWY 9L, WITH A SMALL HELI IN TRAIL APCHING THE FIELD FROM THE W. I HAD NOT YET VISUALLY IDENTED THE P28B. I WAS RESOLVING POTENTIAL CONFLICTS TO THE E, AS WELL AS COORDINATING TURNING AN ACFT THROUGH THE LCL CTL S CTLR'S AIRSPACE WHEN C172 CALLED FOR DEP FROM RWY 9L. I LOOKED AT THE BRITE DISPLAY AND SAW A PRIMARY TARGET ON A 2 MI FINAL FOR RWY 9L AND ASSUMED IT WAS THE P28B. I KNEW THE HELI WAS FLYING AT OR BELOW 500 FT. DUE TO LINE-OF-SIGHT LIMITATIONS, HELIS AT LOW LEVEL OFTENTIMES DO NOT SHOW UP ON RADAR. I ATTRIBUTED THE LACK OF A SECOND TARGET TO THIS FACT. I TOLD THE C172 TO TAXI INTO POS AND HOLD (TFC WAS CLRING DOWNFIELD). FORTUNATELY, THE GND CTLR WAS ALERT AND POINTED OUT THAT THE P28B WAS ON 1/2 MI FINAL. JUST AS I KEYED MY MIKE TO SEND THE P28B AROUND, THE PLT INITIATED A GAR HIMSELF. ADEQUATE SEPARATION WAS MAINTAINED. IN HINDSIGHT, THE PRIMARY TARGET I OBSERVED N THE BRITE DISPLAY WAS THE HELI, AND THE P28B WAS NOT SHOWING UP AT ALL. THE BLIND SPOT HAS BEEN RPTED TO THE APPROPRIATE PERSONNEL, AND SOLUTIONS ARE BEING CONSIDERED.

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.