A B727 DSNDING INTO SLC RECEIVES A TCASII RA AND IMMEDIATELY INCREASES HIS RATE OF DSCNT. AS THE B727 DSNDS IT COMES CLOSE TO A CESSNA CARAVAN. THE CARAVAN COMPLAINS OF THE CLOSE PROX OF THE DSNDING B727. RELIABILITY OF TCASII IS IN QUESTION DURING THIS INCIDENT.

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FLT AA ON JUN/XX/97 FROM YYC TO SLC. I WAS THE FO FLYING AT THE TIME. WE WERE ABOUT 20 MI FROM SLC WITH APCH CTL AT 13000 FT LEVEL; IMC/IFR. WE RECEIVED A TCASII RA COMMANDING AN IMMEDIATE 'DSND' WITH A GREEN ARC ON THE VVI OF MINIMUM 3500 FPM DOWN. AT THE SAME TIME; THERE WAS A DISPLAY OF A TARGET +01 (IN RED) DIRECTLY ABOVE US. THE CAPT CONCURRED AND I BEGAN THE DSCNT. THE CAPT THEN RADIOED ATC AND TOLD THEM OF OUR DSCNT DUE TO A TCASII RA COMMAND. ATC DID NOT RESPOND IMMEDIATELY. WE BROKE OUT OF THE WX AT ABOUT 12300 FT TO SEE A CESSNA CARAVAN TO OUR R ALMOST CO-ALT. WE WERE ON A PARALLEL COURSE; COLLISION WAS NOT A FACTOR. AT THIS TIME; ATC FINALLY ASKED US IF WE HAD THE TFC. WE SAID YES; AND ATC TOLD US TO CLB BACK TO 13000 FT. THE CARAVAN ACKNOWLEDGED SEEING US. PRIOR TO RECEIVING THE TCASII RA COMMAND; THERE WAS NO EARLY 'TFC' WARNING. ATC SHOWED NO OTHER ACFT IN OUR VICINITY. EITHER THERE WAS A TCASII MALFUNCTION; OR ATC DID NOT PICK UP THE TFC CAUSING OUR TCASII RA. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT DURING THE DSCNT THEY WERE SURPRISED AT HOW RAPIDLY THE TCASII 'RA;' WITH NO 'TA' WENT FROM PLUS 3; 2; 1 ON TARGET; TO 'DSND; DSND; DSND.' THE FLC MADE THE DSCNT BUT AS THE DSCNT CONTINUED THROUGH THE CLRED ALT; THEY BROKE OUT OF THE CLOUDS JUST IN TIME TO SEE A CESSNA CARAVAN SOME 500 FT AWAY. THERE WAS NO TCASII RA FOR THIS ACFT. THE CARAVAN SAW THE B727 DSND INTO HIS ALT AND MADE THE COMMENT TO SLC TRACON; 'NICE GOING; SALT LAKE.' THE RPTR'S ACFT CLBED BACK UP TO THE ASSIGNED ALT. NO EVASIVE ACTION WAS TAKEN BY EITHER ACFT. UPON LNDG; THE FLC TALKED WITH TRACON AND LEARNED THAT TRACON NEVER HAD A TARGET IN THE AREA WHEN THEY GOT THE TCASII RA TO CAUSE THE INITIAL DSCNT. TRACON DID HAVE THE CARAVAN TARGET AT ALL TIMES. MAINT INFORMED THE RPTR THAT THEY TOOK THE TCASII UNIT OUT FOR INSPECTION AND THE CARAVAN HAD ITS XPONDER INSPECTED. NO SPECIFIC RESULTS OF ANY EQUIP FAULTS WERE MENTIONED TO THE RPTR. SUPPLEMENTAL INFO FROM ACN 370796: THE VSI'S SIMULTANEOUSLY COMMANDED ABOUT A 3500 FPM DSCNT; AND THE TCASII RA/WX DISPLAY SHOWED A RED TARGET ALMOST COINCIDENTAL WITH OUR POS; AND 300 FT ABOVE (+3) AND DSNDING! AS THE DISPLAY WENT FROM '+2' TO '+1' I COMMANDED THE COPLT; WHO WAS FLYING THE ACFT; TO BEGIN A DSCNT AND SIMULTANEOUSLY INFORMED APCH CTL THAT WE WERE DSNDING IN RESPONSE TO A TCASII RA COMMAND. WE DSNDED TO APPROX 11800 FT. DURING THE DSCNT; THE SO SAW THE RED RA DISAPPEAR AND A YELLOW TARGET APPEAR ACCOMPANIED WITH A 'MONITOR VERT SPD' ANNOUNCEMENT. THE CARAVAN PLT ALSO XMITTED HIS DISPLEASURE WITH THE INCIDENT; RPTING THE SEPARATION AT '70-80 YARDS.' SUPPLEMENTAL INFO FROM ACN 370819: WE DSNDED APPROX 1100 FT. DURING THE DSCNT THE RED RA DISAPPEARED AND A YELLOW TARGET (WITH NO RELATIVE ALT) APPEARED ALONG WITH A 'MONITOR VERT SPD' ANNOUNCEMENT. TOWARDS THE BOTTOM OF OUR DSCNT WE EMERGED FROM THE CLOUDS AND IMMEDIATELY SAW A CESSNA CARAVAN AT OUR ALT ABOUT 1000 FT OFF OUR R WING. THE PNF CALLED THE TFC TO ATC AND RESTATED OUR RA COMMANDED DSCNT. THE CESSNA ALSO CALLED ATC AND STATED THE SEPARATION AS 70-80 YARDS. BY THIS TIME WE HAD PASSED THE CESSNA AND ATC DIRECTED US TO CLB BACK TO 13000 FT. WE CALLED RAPCON AFTER LNDG AND THEY STATED THE CESSNA HAD BEEN LEVEL AT 12000 FT FOR 20 MI.