DSCNT TO OCCUPIED ALT MANDATED BY ALERT WARNING OF TCASII RA WHICH WAS DETERMINED TO BE A FALSE WARNING OR ACFT EQUIP PROB MALFUNCTION. POTENTIAL CONFLICT LTSS.

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WE WERE DSNDING TO 7000 FT INBOUND TO ORD. THE VISIBILITY WAS RESTR (APPROX 2 MI) WITH SCATTERED LAYERED CLOUDS. WE WERE AT 7200 FT DSNDING AT 700 FPM. WE WERE HDG 310 DEGS AND JUST GIVEN A TURN TO 360 DEGS. WE RECEIVED A TA FOLLOWED IMMEDIATELY BY AN RA 'TFC; MONITOR VERT SPD;' FOLLOWED BY 'DSND; XING; DSND.' THIS WAS FOLLOWED ALMOST IMMEDIATELY BY A LOUDER WARNING OF 'INCREASE DSCNT.' WE STARTED A DSCNT OF APPROX 1700 FPM AS WE CONTINUED THE TURN TO 360 DEGS AND NOTIFIED ATC OF OUR DSCNT. WE WERE INFORMED BY THE CTLR THAT OUR TFC WAS BELOW US (WHICH WE KNOW) AND ASKED TO LEVEL. SHORTLY AFTER THAT WE RECEIVED A CLR OF CONFLICT AND LEVELED AT 6100 FT. I FOUND OUT LATER; AFTER TALKING WITH THE CTLR SUPVR; THAT THE CONFLICTING TFC WAS LEVEL AT 6000 FT; AND HAD BEEN FOR SOME TIME. WE WERE MAKING A SMOOTH AND CTLED LEVEL OFF AT 7000 FT. THERE WAS NO REASON; THAT I CAN SEE; FOR THE RA. IN FACT; IT CAUSED A TFC CONFLICT. WE NEVER GAINED VISUAL CONTACT WITH THE OTHER ACFT. SUPPLEMENTAL INFORMATION FROM ACN 240266: I BELIEVE THAT THE TCASII WARNING WAS UNNECESSARY. HAD WE LEVELED AT 7000 FT THERE WOULD NOT HAVE BEEN A PROB. OUR DSCNT RATE TRIGGERED THE CONFLICT WARNING AND ONLY SERVED TO COMPLICATE THE PROB.