Narrative:

We were making a descent into fll and had been cleared by ZMA to depart for 9000 ft when at about 10800 ft I heard a faint aural from the TCASII calling out traffic. I looked at my vvi and saw a target at 12 O'clock at about 700 ft. I alerted the captain who was flying the aircraft and he started to level off. I next saw the target at minus 300 ft and then at our altitude at about 11 O'clock. We were VMC with buildups around us at 6-10 mi. At about that time we got an RA and as I looked up to say something to the captain, I saw the target climb up through our altitude at about 11 O'clock and pass behind us. I reported the traffic to the captain who then idented it as a twin turboprop. We continued our descent to 9000 ft. I asked the center if they had any knowledge of the traffic that had just passed by us at less than a mi and they didn't seem to have any knowledge of it. They asked us what kind it was and we reported it as a twin turboprop. Before we left the frequency, I heard another aircraft ask about what appeared to be the same aircraft. Supplemental information from acn 273795: while conducting radar training with extensive WX deviations and complex radar sits at ZMA, sector R24, I experienced a near midair with air carrier Z. The aircraft reported traffic at his altitude (approximately 12700 ft) at which time I displayed and issued traffic '12 O'clock 1 mi indicating 10400 ft.' this target was displayed as a 'V104' which was very confusing to myself. Traffic at this altitude should be displayed as 'I104.' this is called a mode C intruder. I was then informed by this air carrier Z that 'no, the traffic is at our altitude' (approximately 12300 ft). I cleared air carrier Z to take any maneuvers necessary to miss the traffic. Approximately 10 mi in trail was another air carrier X aircraft. I asked the first air carrier Z what type aircraft the target was and he said 'king air type.' I then issued the traffic to the second aircraft X at 12 O'clock, 8 mi indicating 12700 ft (K127). He reported looking for traffic at which time I completely lost the target, code and altitude of the VFR traffic and I informed the aircraft that I was no longer displaying the traffic. Shortly after this the second air carrier X reported visual at '113 or 114' and not a factor. I was amazed that I did not even display a target. The first air carrier Z landed at fll and filed a near midair collision report. My radar did not adequate display the mode C of the traffic. I'm curious to know what air carrier Z TCASII displayed concerning the traffic's altitude.

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Original NASA ASRS Text

Title: LGT X TAKES EVASIVE ACTION OF LEVELOFF WHEN TCASII INDICATES TFC. LGT Z AHEAD, EXPERIENCES NMAC WITH SAME TWIN, ACFT Y. SIMULTANEOUS LOSS OF ACFT RETURN ON ARTCC RADAR ACFT TCASII.

Narrative: WE WERE MAKING A DSCNT INTO FLL AND HAD BEEN CLRED BY ZMA TO DEPART FOR 9000 FT WHEN AT ABOUT 10800 FT I HEARD A FAINT AURAL FROM THE TCASII CALLING OUT TFC. I LOOKED AT MY VVI AND SAW A TARGET AT 12 O'CLOCK AT ABOUT 700 FT. I ALERTED THE CAPT WHO WAS FLYING THE ACFT AND HE STARTED TO LEVEL OFF. I NEXT SAW THE TARGET AT MINUS 300 FT AND THEN AT OUR ALT AT ABOUT 11 O'CLOCK. WE WERE VMC WITH BUILDUPS AROUND US AT 6-10 MI. AT ABOUT THAT TIME WE GOT AN RA AND AS I LOOKED UP TO SAY SOMETHING TO THE CAPT, I SAW THE TARGET CLB UP THROUGH OUR ALT AT ABOUT 11 O'CLOCK AND PASS BEHIND US. I RPTED THE TFC TO THE CAPT WHO THEN IDENTED IT AS A TWIN TURBOPROP. WE CONTINUED OUR DSCNT TO 9000 FT. I ASKED THE CTR IF THEY HAD ANY KNOWLEDGE OF THE TFC THAT HAD JUST PASSED BY US AT LESS THAN A MI AND THEY DIDN'T SEEM TO HAVE ANY KNOWLEDGE OF IT. THEY ASKED US WHAT KIND IT WAS AND WE RPTED IT AS A TWIN TURBOPROP. BEFORE WE LEFT THE FREQ, I HEARD ANOTHER ACFT ASK ABOUT WHAT APPEARED TO BE THE SAME ACFT. SUPPLEMENTAL INFO FROM ACN 273795: WHILE CONDUCTING RADAR TRAINING WITH EXTENSIVE WX DEVS AND COMPLEX RADAR SITS AT ZMA, SECTOR R24, I EXPERIENCED A NEAR MIDAIR WITH ACR Z. THE ACFT RPTED TFC AT HIS ALT (APPROX 12700 FT) AT WHICH TIME I DISPLAYED AND ISSUED TFC '12 O'CLOCK 1 MI INDICATING 10400 FT.' THIS TARGET WAS DISPLAYED AS A 'V104' WHICH WAS VERY CONFUSING TO MYSELF. TFC AT THIS ALT SHOULD BE DISPLAYED AS 'I104.' THIS IS CALLED A MODE C INTRUDER. I WAS THEN INFORMED BY THIS ACR Z THAT 'NO, THE TFC IS AT OUR ALT' (APPROX 12300 FT). I CLRED ACR Z TO TAKE ANY MANEUVERS NECESSARY TO MISS THE TFC. APPROX 10 MI IN TRAIL WAS ANOTHER ACR X ACFT. I ASKED THE FIRST ACR Z WHAT TYPE ACFT THE TARGET WAS AND HE SAID 'KING AIR TYPE.' I THEN ISSUED THE TFC TO THE SECOND ACFT X AT 12 O'CLOCK, 8 MI INDICATING 12700 FT (K127). HE RPTED LOOKING FOR TFC AT WHICH TIME I COMPLETELY LOST THE TARGET, CODE AND ALT OF THE VFR TFC AND I INFORMED THE ACFT THAT I WAS NO LONGER DISPLAYING THE TFC. SHORTLY AFTER THIS THE SECOND ACR X RPTED VISUAL AT '113 OR 114' AND NOT A FACTOR. I WAS AMAZED THAT I DID NOT EVEN DISPLAY A TARGET. THE FIRST ACR Z LANDED AT FLL AND FILED A NMAC RPT. MY RADAR DID NOT ADEQUATE DISPLAY THE MODE C OF THE TFC. I'M CURIOUS TO KNOW WHAT ACR Z TCASII DISPLAYED CONCERNING THE TFC'S ALT.

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.