LGT HAS TCASII TA IN IMC. INDICATES CLOSE PROX BUT NO RA.

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AN AIRBUS 320 WAS ON FINAL APCH TO DCA RWY 36. THE CREW WAS IN IMC CONDITIONS INFLUENCED BY A STRONG EASTERLY WIND FLOW AT THE TIME OF THE OCCURRENCE. ACFT X WAS FOLLOWING ANOTHER ACFT TO THE ARPT. AN ACFT WAS TAKEN OFF THE APCH BY THE APCH CTLR DUE TO AN IMPENDING SEPARATION CONFLICT. ACFT X WAS TOLD TO CONTACT DCA TWR. AFTER APPROX 30 SECONDS WITH THE TWR; DCA TWR BROKE ACFT X OFF THE FINAL APCH COURSE DUE TO ANOTHER IMPENDING SEPARATION CONFLICT. TWR GAVE ACFT X A TURN TO 270 DEGS AND HANDED THEM OFF TO DEP CTL. DEP GAVE ACFT X A TURN TO 160 DEGS WHICH ESTABLISHED THE ACFT ON DOWNWIND AT 3000 FT MSL. THE CREW OBSERVED A TA ON THE TCASII TO BE JUST OUTSIDE OF THE TCASII 10 MI RANGE. THE INTRUDER APPEARED AT 11 O'CLOCK; 900 FT ABOVE THEIR ALT AND DSNDING. DEP WAS QUERIED ABOUT ANY TFC IN THE AREA. THERE WAS NO RESPONSE FROM ATC. A SECOND QUERY WAS MADE TO ATC; AGAIN; NO RESPONSE. AT THAT TIME; THE CREW OBSERVED THE TA TOUCH THE TCASII SYMBOLIC ACFT'S L WING. THE LAST OBSERVED ALT READOUT ON THE INTRUDER WAS 200 FT AND DSNDING. DEP THEN GAVE ACFT X A TURN TO 270 DEGS FOLLOWED BY A TURN BACK ONTO FINAL. THE CREW THEN MADE AN UNEVENTFUL LNDG AT DCA. UPON ARRIVING AT THE GATE AT DCA THE CREW CALLED THE DCA APCH CTL FACILITY. THE CREW WAS TOLD TO CALL BACK LATER. WHEN THE CREW CALLED BACK LATER; THEY SPOKE WITH MR. A; SUPVR; ATC DCA APCH CTL. MR. A INFORMED CAPT THAT HE HAD ALREADY SPOKEN WITH ATC QUALITY CTL PERSONNEL AND THAT THERE HAD NOT BEEN A CONFLICT. MR. A INDICATED THAT THE 'SNITCH' SYS HAD NOT GIVEN AN ALARM DURING THE TIME OF THE OCCURRENCE. MR. A INDICATED THAT THE TCASII OBSERVED TFC WAS A DHC-8 OPERATING UNDER ATC CTL. CAPT REQUESTED THAT ATC 'PULL THE TAPES.' CAPT NOTIFIED COMPANY THROUGH THE SECRETARY FOR A320 FLEET MGR. SUBSEQUENTLY; CAPT MADE CONTACT WITH FLEET MGR AND EXPRESSED HIS CONCERN OVER NOT ONLY THE NEAR MISS; BUT THE LACK OF THE A320'S TCASII SYS TO PROVIDE AN RA DURING THE OCCURRENCE.