Narrative:

Approximately 20 NM west of mia on a 120 degree heading to intercept the 9L localizer and descending to 3000 MSL, mia approach requested we turn to 090 degrees and reported traffic at our 11 O'clock altitude unknown. As we rolled out 090 degrees, we had neither a visual sighting nor TCASII contact with the traffic. Passing 4000 MSL, TCASII gave a TA and suddenly displayed an amber target at 11 O'clock -- 800 ft and 4 NM. This was followed immediately with an RA commanding a level-off on the vvi. The first officer was flying and responded immediately by leveling the aircraft at 3200 MSL. Simultaneous with the 'monitor vertical speed' RA I acquired the traffic visually 2-3 NM and converging. As it appeared we would pass close, I told my first officer to 'climb to 3500.' as he leveled at 3500 MSL the traffic passed directly beneath us with 500 ft of vertical separation according to the TCASII. When I advised mia approach we had a TCASII RA on the traffic they replied that they were receiving no transponder code from the aircraft. I suspect the traffic's transponder was not operating properly, responding to interrogations with a weak reply that could not be received by approach control and was not picked up by our TCASII until inside of 4 NM. The traffic was a single engine low wing, light brown with dark markings. Its pilot apparently never saw us as he took no evasive action. Clear of traffic, we continued our descent, and were cleared by approach to return to our intercept of the localizer. TCASII gets my vote. Still, 'see and avoid' is the best course of action.

Related reports:

Google
 

Original NASA ASRS Text

Title: LGT HAS NMAC WITH SMA ON DSCNT.

Narrative: APPROX 20 NM W OF MIA ON A 120 DEG HDG TO INTERCEPT THE 9L LOC AND DSNDING TO 3000 MSL, MIA APCH REQUESTED WE TURN TO 090 DEGS AND RPTED TFC AT OUR 11 O'CLOCK ALT UNKNOWN. AS WE ROLLED OUT 090 DEGS, WE HAD NEITHER A VISUAL SIGHTING NOR TCASII CONTACT WITH THE TFC. PASSING 4000 MSL, TCASII GAVE A TA AND SUDDENLY DISPLAYED AN AMBER TARGET AT 11 O'CLOCK -- 800 FT AND 4 NM. THIS WAS FOLLOWED IMMEDIATELY WITH AN RA COMMANDING A LEVEL-OFF ON THE VVI. THE FO WAS FLYING AND RESPONDED IMMEDIATELY BY LEVELING THE ACFT AT 3200 MSL. SIMULTANEOUS WITH THE 'MONITOR VERT SPD' RA I ACQUIRED THE TFC VISUALLY 2-3 NM AND CONVERGING. AS IT APPEARED WE WOULD PASS CLOSE, I TOLD MY FO TO 'CLB TO 3500.' AS HE LEVELED AT 3500 MSL THE TFC PASSED DIRECTLY BENEATH US WITH 500 FT OF VERT SEPARATION ACCORDING TO THE TCASII. WHEN I ADVISED MIA APCH WE HAD A TCASII RA ON THE TFC THEY REPLIED THAT THEY WERE RECEIVING NO XPONDER CODE FROM THE ACFT. I SUSPECT THE TFC'S XPONDER WAS NOT OPERATING PROPERLY, RESPONDING TO INTERROGATIONS WITH A WEAK REPLY THAT COULD NOT BE RECEIVED BY APCH CTL AND WAS NOT PICKED UP BY OUR TCASII UNTIL INSIDE OF 4 NM. THE TFC WAS A SINGLE ENG LOW WING, LIGHT BROWN WITH DARK MARKINGS. ITS PLT APPARENTLY NEVER SAW US AS HE TOOK NO EVASIVE ACTION. CLR OF TFC, WE CONTINUED OUR DSCNT, AND WERE CLRED BY APCH TO RETURN TO OUR INTERCEPT OF THE LOC. TCASII GETS MY VOTE. STILL, 'SEE AND AVOID' IS THE BEST COURSE OF ACTION.

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.