Narrative:

We were on the blitho 5 arrival to kmco and was cleared to cross lamma intersection at 12000 ft and 250 KTS. At omn 176 degree/05 we were descending through 17000 ft at 300 KTS and approximately 2000 FPM descent when our TCASII sounded 'traffic.' we then noticed the traffic on our screen for the first time at our 12 O'clock position approximately 3 NM range. My scope was set at the 10 mi range and this traffic did not show up prior to this. Simultaneously with the TCASII TA jax center advised us of traffic at our 12 O'clock position and unconfirmed altitude of 16600 ft. Within a second or 2 our TCASII called 'descend, descend now' along with a 2500 FPM min descent rate command. Our altitude was then going through 16600 ft and my copilot who was flying initiated a diving right turn, I last noticed the traffic on our TCASII screen at less than a mi and at our altitude. All this took place in what seemed like 5 or 6 seconds. This resulted in a very uncomfortable diving right turn at 4000 FPM rate of descent. I never did see the traffic visually. Upon arrival at kmco I called jax center and they confirmed that there was indeed an small aircraft flying VFR at that position. The small aircraft had to have had an operating transponder with altitude encoder to show up on our TCASII screen as it did. Why didn't the TCASII alert sound earlier? Why didn't we get an earlier advisory from center? Prior to and subsequent to this event our TCASII system operated properly. Did the small aircraft just then turn on his transponder? Whatever the reason, TCASII does work and has found another believer in the system.

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Original NASA ASRS Text

Title: TCASII RA TFC VERY CLOSE. CENTER CALLED TFC.

Narrative: WE WERE ON THE BLITHO 5 ARR TO KMCO AND WAS CLRED TO CROSS LAMMA INTXN AT 12000 FT AND 250 KTS. AT OMN 176 DEG/05 WE WERE DSNDING THROUGH 17000 FT AT 300 KTS AND APPROX 2000 FPM DSCNT WHEN OUR TCASII SOUNDED 'TFC.' WE THEN NOTICED THE TFC ON OUR SCREEN FOR THE FIRST TIME AT OUR 12 O'CLOCK POS APPROX 3 NM RANGE. MY SCOPE WAS SET AT THE 10 MI RANGE AND THIS TFC DID NOT SHOW UP PRIOR TO THIS. SIMULTANEOUSLY WITH THE TCASII TA JAX CENTER ADVISED US OF TFC AT OUR 12 O'CLOCK POS AND UNCONFIRMED ALT OF 16600 FT. WITHIN A SECOND OR 2 OUR TCASII CALLED 'DSND, DSND NOW' ALONG WITH A 2500 FPM MIN DSCNT RATE COMMAND. OUR ALT WAS THEN GOING THROUGH 16600 FT AND MY COPLT WHO WAS FLYING INITIATED A DIVING R TURN, I LAST NOTICED THE TFC ON OUR TCASII SCREEN AT LESS THAN A MI AND AT OUR ALT. ALL THIS TOOK PLACE IN WHAT SEEMED LIKE 5 OR 6 SECONDS. THIS RESULTED IN A VERY UNCOMFORTABLE DIVING R TURN AT 4000 FPM RATE OF DSCNT. I NEVER DID SEE THE TFC VISUALLY. UPON ARR AT KMCO I CALLED JAX CENTER AND THEY CONFIRMED THAT THERE WAS INDEED AN SMA FLYING VFR AT THAT POS. THE SMA HAD TO HAVE HAD AN OPERATING TRANSPONDER WITH ALT ENCODER TO SHOW UP ON OUR TCASII SCREEN AS IT DID. WHY DIDN'T THE TCASII ALERT SOUND EARLIER? WHY DIDN'T WE GET AN EARLIER ADVISORY FROM CENTER? PRIOR TO AND SUBSEQUENT TO THIS EVENT OUR TCASII SYS OPERATED PROPERLY. DID THE SMA JUST THEN TURN ON HIS TRANSPONDER? WHATEVER THE REASON, TCASII DOES WORK AND HAS FOUND ANOTHER BELIEVER IN THE SYS.

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.