Narrative:

On vectors for a runway 9L localizer intercept, while on descent to 4000 ft at approximately 4500 ft, approach asked us if we saw a target he painted ahead and on our right climbing and heading toward us. We did not. As he asked us if we would like a vector around him, we go the climb RA. We advised we were responding to the RA, and climbing. Following the top of the green arc climb was not allowing us to get away from the target, so we increased climb above green arc to maximum climb. Traffic continued to climb with us at about 480 ft below us all the way to 8000 ft. Target then passed beneath us from nose right to tail left. Approach asked us to get a sighting on him, but in a nose high attitude, and as close as he was to us we were unable. As TCASII showed, he cleared underneath us on our rear left side. ATC also confirmed he had cleared us. No ordinary light plane could have possibly kept up with us on our maximum performance climb. To have kept up with our climb to 8000 ft he must have been military, cpr jet, or a very high performance civilian aircraft. Supplemental information from acn 583877: I was in jump seat #1. Sudden ascent and turn to the right then hard bank to the left. Captain came on the PA within 5 mins told all that 'there was a small aircraft without a transponder and was too close to us.' after all passenger were off the aircraft, captain told us that the small aircraft was within 400 ft. He said that when we turned right, the aircraft followed us so we turned left and the aircraft passed us. I don't think any passenger saw the aircraft. Sure would like to know who was flying the small aircraft without communicating with the tower or other aircraft. They were ascending into our route to mia.

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Original NASA ASRS Text

Title: NMAC BTWN A DSNDING B757 AND A CLBING HIGH PERFORMANCE JET IN THE CLASS B AIRSPACE APPROX 15 NM NW OF MIA, FL.

Narrative: ON VECTORS FOR A RWY 9L LOC INTERCEPT, WHILE ON DSCNT TO 4000 FT AT APPROX 4500 FT, APCH ASKED US IF WE SAW A TARGET HE PAINTED AHEAD AND ON OUR R CLBING AND HEADING TOWARD US. WE DID NOT. AS HE ASKED US IF WE WOULD LIKE A VECTOR AROUND HIM, WE GO THE CLB RA. WE ADVISED WE WERE RESPONDING TO THE RA, AND CLBING. FOLLOWING THE TOP OF THE GREEN ARC CLB WAS NOT ALLOWING US TO GET AWAY FROM THE TARGET, SO WE INCREASED CLB ABOVE GREEN ARC TO MAX CLB. TFC CONTINUED TO CLB WITH US AT ABOUT 480 FT BELOW US ALL THE WAY TO 8000 FT. TARGET THEN PASSED BENEATH US FROM NOSE R TO TAIL L. APCH ASKED US TO GET A SIGHTING ON HIM, BUT IN A NOSE HIGH ATTITUDE, AND AS CLOSE AS HE WAS TO US WE WERE UNABLE. AS TCASII SHOWED, HE CLRED UNDERNEATH US ON OUR REAR L SIDE. ATC ALSO CONFIRMED HE HAD CLRED US. NO ORDINARY LIGHT PLANE COULD HAVE POSSIBLY KEPT UP WITH US ON OUR MAX PERFORMANCE CLB. TO HAVE KEPT UP WITH OUR CLB TO 8000 FT HE MUST HAVE BEEN MIL, CPR JET, OR A VERY HIGH PERFORMANCE CIVILIAN ACFT. SUPPLEMENTAL INFO FROM ACN 583877: I WAS IN JUMP SEAT #1. SUDDEN ASCENT AND TURN TO THE R THEN HARD BANK TO THE L. CAPT CAME ON THE PA WITHIN 5 MINS TOLD ALL THAT 'THERE WAS A SMALL ACFT WITHOUT A XPONDER AND WAS TOO CLOSE TO US.' AFTER ALL PAX WERE OFF THE ACFT, CAPT TOLD US THAT THE SMALL ACFT WAS WITHIN 400 FT. HE SAID THAT WHEN WE TURNED R, THE ACFT FOLLOWED US SO WE TURNED L AND THE ACFT PASSED US. I DON'T THINK ANY PAX SAW THE ACFT. SURE WOULD LIKE TO KNOW WHO WAS FLYING THE SMALL ACFT WITHOUT COMMUNICATING WITH THE TWR OR OTHER ACFT. THEY WERE ASCENDING INTO OUR RTE TO MIA.

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.