Narrative:

Cruising at FL210, 98 NM northwest of stl on the uin 143 degree radial, rivers 1 arrival to stl. ZKC directed a descent to FL190. As PNF acknowledged, PF initiated descent. As aircraft passed FL206, TCASII audio of 'traffic, traffic' occurred. I checked the TCASII display and noted the traffic symbol at the 0930 to 10 O'clock position, approximately 3 mi, 700 ft below and level. As I looked outside in an attempt to sight the traffic, the TCASII system issued a 'climb, climb' audio RA and the display indicated a min 2000 FPM climb. The aircraft was at FL205 at this time and the traffic symbol on TCASII was at the 9 to 0930 O'clock position, 500 ft below and level, approximately 2 1/2 mi. I told the PF that I didn't have sight of the traffic and he immediately started a climb. I notified center we had an RA on the traffic at 9 O'clock, which I had spotted as I was talking to them. The aircraft was a twin engine, propeller at approximately FL200. Center controller directed us to maintain FL210 and a short time later, asked if we had descended below FL210. I said that we had reached FL205 before climbing back to FL210. The traffic passed behind us at approximately 2 NM at the closest point. Supplemental information from acn 284951: we picked up the aircraft visually and did not consider the incident to be a near miss. Lowest altitude we went to was 19600 ft. I think the other aircraft was an IFR king air at FL200.

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Original NASA ASRS Text

Title: OPERROR TCASII ALERT.

Narrative: CRUISING AT FL210, 98 NM NW OF STL ON THE UIN 143 DEG RADIAL, RIVERS 1 ARR TO STL. ZKC DIRECTED A DSCNT TO FL190. AS PNF ACKNOWLEDGED, PF INITIATED DSCNT. AS ACFT PASSED FL206, TCASII AUDIO OF 'TFC, TFC' OCCURRED. I CHKED THE TCASII DISPLAY AND NOTED THE TFC SYMBOL AT THE 0930 TO 10 O'CLOCK POS, APPROX 3 MI, 700 FT BELOW AND LEVEL. AS I LOOKED OUTSIDE IN AN ATTEMPT TO SIGHT THE TFC, THE TCASII SYS ISSUED A 'CLB, CLB' AUDIO RA AND THE DISPLAY INDICATED A MIN 2000 FPM CLB. THE ACFT WAS AT FL205 AT THIS TIME AND THE TFC SYMBOL ON TCASII WAS AT THE 9 TO 0930 O'CLOCK POS, 500 FT BELOW AND LEVEL, APPROX 2 1/2 MI. I TOLD THE PF THAT I DIDN'T HAVE SIGHT OF THE TFC AND HE IMMEDIATELY STARTED A CLB. I NOTIFIED CTR WE HAD AN RA ON THE TFC AT 9 O'CLOCK, WHICH I HAD SPOTTED AS I WAS TALKING TO THEM. THE ACFT WAS A TWIN ENG, PROP AT APPROX FL200. CTR CTLR DIRECTED US TO MAINTAIN FL210 AND A SHORT TIME LATER, ASKED IF WE HAD DSNDED BELOW FL210. I SAID THAT WE HAD REACHED FL205 BEFORE CLBING BACK TO FL210. THE TFC PASSED BEHIND US AT APPROX 2 NM AT THE CLOSEST POINT. SUPPLEMENTAL INFO FROM ACN 284951: WE PICKED UP THE ACFT VISUALLY AND DID NOT CONSIDER THE INCIDENT TO BE A NEAR MISS. LOWEST ALT WE WENT TO WAS 19600 FT. I THINK THE OTHER ACFT WAS AN IFR KING AIR AT FL200.

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.