ALT SEPARATION REDUCED DURING FALSE LOGIC RA BY TCASII IN DSNDING XING TFC SIT.

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WE WERE DSNDING TO FL290 AND OUR TFC WAS AT FL280. I WAS IN THE R SEAT WHEN TFC WAS POINTED OUT AT OUR 3 O'CLOCK POS. I IMMEDIATELY GAINED VISUAL CONTACT AND SAW THE TFC WOULD PASS WELL CLR BEHIND. I RESUMED MY XCHK INSIDE (I WAS FLYING) WHEN WE GOT A TA ADVISING US TO 'REDUCE DSCNT.' APPROX 10 SECONDS LATER; WE GOT AN RA ADVISING US TO 'DSND; DSND;' SO I IMMEDIATELY LOOKED BACK OUTSIDE TO VERIFY TFC; BUT HE WAS BEHIND HEAVIER CIRRUS NOW. SINCE WE DIDN'T HAVE VISUAL ON THE TFC; WE WERE OBLIGED TO KEEP DSNDING PER TCASII. ALL OF THIS WAS HAPPENING VERY RAPIDLY. WE DSNDED TO FL286 UNTIL THE RA WENT AWAY THEN CLBED BACK UP TO FL290. WE NOTICED ON TCASII THAT TFC CAME NO CLOSER THAN 3 1/2 MI. SIDE NOTES: TCASII NEEDED 2 TRIES TO PASS BITE TEST DURING OUR PREFLT. ON SECOND LEG; BOTH RADAR ALTIMETERS WERE TEMPORARILY LOST; GPWS WAS LOST; AND TCASII WAS INOP -- ALL FOR APPROX 5 MINS. DUE TO THIS FACT AND CONFLICTING INFO TCASII GAVE US ON DSCNT INTO SAN; TCASII WAS DISABLED AND FLT WAS CONTINUED PER THE MEL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE ACFT WAS A B-737-300 AND HAD THE INITIAL TCASII RA LOGIC PROB GOING INTO SAN. THE ACFT LATER HAD A PROB WITH THE GPWS AND 2 RADIO ALTIMETERS GOING FROM SAN TO SFO. THERE; THE ACFT'S TCASII WAS MEL'ED AND A REVISED DISPATCH RELEASE OBTAINED. THE ACFT WAS FLOWN TO PHX WHERE MAINT LOOKED AT THE ACFT. RPTR IS NOT AWARE OF MAINT FINDINGS AT PHX. HE STATED THAT THE FIRST 'SELF TEST' WAS PERFORMED ERRONEOUSLY. THE IRS UNITS HAD NOT GOTTEN UP TO SPD AS YET SO THE FIRST TEST FAILED. THE SECOND TEST FAILED LATER; WITH NO 'MESSAGES' BEING DISPLAYED. THE THIRD SELF TEST WAS SUCCESSFUL. HE FURTHER STATED THAT THE ACR WAS 'STAYING ON TOP OF THE PROB' DURING THESE FLTS.