ACR X DURING DSCNT TO 5000 FT RECEIVED TCASII TA ACFT AT 5500 FT ADDITIONAL TCASII RA WITH ACFT Y AT 4500 FT. ACR X HAD NMAC WITH ACFT Y. SEE AND AVOID CONCEPT.

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ACR X; YYC TO GEG; ON APCH INTO GEG; VMC; CLRED TO DSND TO 5000 FT. PASSING 7000 FT; APCH CALLED TFC AT 5500 FT; 12 O'CLOCK HOLDING OVER 'PHORT' NDB. TCASII CONFIRMED AND VISUAL CONTACT WAS MADE. TCASII GAVE TA TO SIGHTED TFC; AND ATC TOLD US TO EXPEDITE TO 5000 FT. AT 5200 FT; A SECOND TCASII TARGET APPEARED; -600 FT; 12 O'CLOCK; WITH THE TCASII SYMBOLS FOR THE SIGHTED TFC AND THE UNANNOUNCED (BY ATC) OTHER ACFT Y ALMOST SUPERIMPOSED. TCASII GAVE AN RA; 'CLB;' SO WE STOPPED OUR DSCNT; LOOKING FOR THE NEW TARGET. IT WAS NOT SEEN; BUT TCASII INDICATED -100 FT ON OUR POS. THE ENTIRE EPISODE; FROM LEVEL AT 5000 FT TO 'CLR OF CONFLICT;' TOOK 15 SECONDS. WE WERE RELUCTANT TO CLB BECAUSE THE SIGHTED ACFT; WHICH HAD PASSED OUT OF VIEW DOWN OUR L SIDE; WAS AT 5200 FT AND THE UNRPTED (BY ATC); UNSIGHTED WAS CONSIDERED WE DIDN'T WANT TO CLB BACK INTO A CONFLICT. WE CALLED ARPT IN SIGHT AND WERE CLRED FOR VISUAL TO RWY 21. WE WERE NOT AWARE OF THE UNRPTED TFC; AND HAD NO VISUAL ON IT; SO WE BEGAN A SHALLOW DSCNT TOWARDS THE GS. WE WERE UNCERTAIN OF THE EXISTENCE OF THE UNRPTED TARGET; WITH ITS SYMBOL VERY CLOSE TO THE KNOWN TFC SYMBOL. AT THE POINT OF CLOSURE; WE HAD 2 RED SYMBOLS; BUT HAD SEEN THE TARGET RPTED BY ATC; AND FELT IT WAS POSSIBLE A PHANTOM IMAGE MIGHT HAVE OCCURRED. PHONE CONVERSATION BTWN THE CAPT AND ATC CONFIRMED 2 TARGETS; WITH ATC TRYING TO PUT OUR LGT AT 5000 FT ON APCH BTWN 2 VFR ACFT; ONE AT 4500 FT TRANSITING THE AREA; AND THE 2ND AT 5500 FT.