PLTDEV OCCURS WHEN THE FLC OF WDB ACR RECEIVES A TCASII RA AND DSNDS CLBS TO AVOID TFC DSNDING FROM ABOVE TO BELOW THEM. ATC DOES NOT PAINT THIS TARGET. THE TFC IS NOT SIGHTED BY THE CREW.

Narrative

WE WERE LEVEL 8000 FT ON AN ASSIGNED HDG TALKING TO SLC DEP. ATC ADVISED US OF TFC AT 11 O'CLOCK 500 FT BELOW US. I LOOKED AT TCASII DISPLAY AND NOTED 2 TARGETS; ONE 500 FT LOW AND #2 TARGET 500 FT ABOVE AT 12:30 POS. ATC CLRED US TO CLB TO FL230. HESITATED DUE TO 500 FT HIGH TFC. I BELIEVE I DID SLOWLY GET UP TO 8100 FT WHILE DISCUSSING TFC WITH CAPT. TCASII GAVE RA 'DSND.' WITH CAPT'S CONCURRENCE INITIATED DSCNT. CONTINUED CLOSING WITH BOTH TARGETS OF WHICH #2 APPEARED TO HAVE CLOSEST CPA. THE #2 TARGET HAD INITIATED DSCNT AT A HIGHER RATE THAN US. AT 7500 FT CAPT NOTIFIED ATC THAT WE WERE FOLLOWING A TCASII RA. ATC SAID THAT THE TFC HAD US IN SIGHT AND WAS DSNDING. (ATC APPARENTLY NEVER HAD RADAR CONTACT ON THE TARGET; WE WERE MANEUVERING TO AVOID.) AT 7500 FT AS THE CAPT WAS TALKING TO ATC BECAUSE THE #2 TARGET WAS NOW APPARENTLY BELOW US THE TCASII GAVE A 'CLB' RA. WE REVERSED OUR DSCNT AND CLBED. THE CAPT DID GET A VISUAL CONTACT ON THE #1 TARGET AS IT PASSED LOW L. WE NEVER VISUALLY SIGHTED THE #2 TARGET; HOWEVER; WE NEVER REALLY LOOKED FOR IT THAT HARD AS I WAS BUSY FOLLOWING MY TCASII COMMANDS ON THE VSI AND THE CAPT WAS TALKING AND LOOKING FOR #1. EITHER OUR TCASII WAS GIVING US A BOGUS CONTACT OR ATC'S RADAR NEEDS SOME TWEAKING. SUPPLEMENTAL INFO FROM ACN 325211: APCH CTL RPTED ONLY PAINTING 1 TARGET FOR US (APPARENTLY THE TFC AT 11 O'CLOCK).