ACR X HAD NMAC. VFR SMA Y IN TCA. ACR X TCASII RA WRONG INSTRUCTIONS DSND FOLLOWED BY CLB. EVASIVE ACTION TAKEN.

Narrative

ACR X ON RADAR VECTORS FOR A VISUAL APCH TO RWY 33. FOLLOWING THE CTLR'S INSTRUCTIONS; WE WERE ON A SOUTHERLY HDG AT 4000 FT. THE CTLR THEN ISSUED A CLRNC TO TURN TO A SW HDG AND DSND TO 2500; TO WHICH THE COPLT RESPONDED IMMEDIATELY TO BY UTILIZING AN AUTOPLT DSCNT. AS WE WERE GOING THROUGH 3700; THE CTLR THEN XMITTED 'ON SECOND THOUGHT; MAINTAIN 4000; TFC AT (TO THE BEST OF MY MEMORY) 11 O'CLOCK; 3 MI; AT 3500'. NO TFC WAS SHOWING ON THE TCASII WHICH WAS OPERATING IN TA/RA MODE AND 10 MI SCALE. I RESPONDED TO HER; 'ROGER; WE'LL CLB BACK TO 4000' AS THE COPLT DISCONNECTED THE AUTOPLT AND BEGAN A MANUAL CLB BACK TO 4000 FT. AT THAT MOMENT; I NOTICED POP-UP TFC ON THE TCASII; SLIGHTLY L OF THE NOSE; CLOSE IN (PERHAPS 2 MI) AND SHOWING A '-1' READOUT. JUST THEN; THE TCASII ISSUED THE FOLLOWING COMMANDS: 'TFC; TFC'; FOLLOWED IMMEDIATELY BY 'DSND; DSND'. THE VERT SPD LIGHTS SHOWED THE NEED FOR A DSCNT IN EXCESS OF 2000 FPM. I IMMEDIATELY TOOK THE ACFT FROM THE COPLT; PULLED BACK THE PWR AND PUSHED THE NOSE OVER. WITHIN APPROX 2 SECONDS OF THE DSND COMMAND; THE TCASII THEN COMMANDED 'CLB; CLB' AND DISPLAYED A REQUIRED CLB RATE IN EXCESS OF 2000 FPM. I IMMEDIATELY REVERSED DIRECTION BY PUSHING UP THE PWR AND PULLING BACK ON THE WHEEL. ABOUT THAT TIME I CAUGHT SIGHT OF AN SMA Y PASSING SLIGHTLY TO OUR L AND APPROX 200-300 FT BELOW US. IN MY OPINION; IF I HAD CONTINUED TO FOLLOW THE FIRST TCASII COMMAND RATHER THAN IMMEDIATELY CHANGING DIRECTION WITH THE SECOND COMMAND; WE WOULD HAVE HIT THE TFC. WE THEN ENTERED THE VFR PATTERN AND LANDED UNEVENTFULLY AT BWI. DISCUSSING THIS EVENT AFTER LNDG WITH THE BWI SUPVR VIA TELEPHONE; THE SUPVR TOLD ME THAT THE CTLR ADMITTED THAT IT HAD BEEN COMPLETELY HER ERROR; THAT SHE HAD 'FORGOTTEN ABOUT' THE VFR TFC WHEN SHE ISSUED OUR DSCNT CLRNC FROM 4000. SUPPLEMENTAL INFO FROM ACN 223101. ACR X WAS ISSUED A CLB TO MAINTAIN 4000 FT. SMA Y WAS ISSUED A DSCNT FROM 3500 FT TO 2500 FT. ACR X RPTED A TCASII ALERT.