ACR X TCASII RA HAD LTSS WITH ACR Y. EVASIVE ACTION TAKEN. SYS ERROR.

Narrative

ACR X TOLD TO EXPECT RWY 18R. LATER; WE WERE GIVEN A SECOND APCH FREQ -- SECOND FREQ VERY BUSY -- UNABLE TO CHK IN -- FIRST COM WAS WHEN APCH ASSIGNED A 270 DEG HDG. WE HAD BEEN ON A 355 HDG. OUR CALL SIGN ACR X SIMILAR COMPANY NUMBERS ALSO ON THE FREQ. NEXT; WE WERE GIVEN A L TURN TO INTERCEPT LOC FOR 18L. WE INQUIRED AS TO RWY AND COMPANY ANSWERED. WE THEN HAD A TCASII ALERT TO 'CLB.' WE INITIATED IMMEDIATE CLB -- CAPT AND SO SAW ONCOMING TURBOPROP OPPOSITE DIRECTION; 100 FT BELOW IN STEEP R TURN. APCH ALSO GAVE A TURN TO 090; WHICH WAS PARTIALLY BLOCKED -- MUCH CONFUSION ON FREQ -- EVERYONE TALKING. WE WERE THEN TOLD THE RWY WAS TO BE 18R AGAIN. WE ADVISED APCH WE HAD CLBED WITH A TCASII WARNING TO AVOID TFC. SHE ACKNOWLEDGED AND THEN ISSUED US A VISUAL APCH TO RWY 18L! WITH THE INITIAL CONFUSION OF WHICH RWY; WITH A CLRNC TO INTERCEPT LOC; OUR ATTN WAS DIVERTED TO DISCUSSION OF PREVIOUS ASSIGNED RWY AND LOOKING UP NEW LOC FREQ. OUR LOOK-SEE-AVOID WAS NOW INOP. WITHOUT TCASII; WE MAY HAVE HAD A MUCH DIFFERENT OUTCOME. AFTER FOLLOW-UP PHONE CALLS TO APCH AT MEM; WE WERE INFORMED THAT THE COMPUTER GENERATED WARNING OF CONFLICT WAS OTS. ALL THINGS COMBINED THIS WAS NOT A GOOD SIT. SUPPLEMENTAL INFO FROM ACN 246633: WE WERE ACR X. THERE WAS SIMILAR NUMBER ON SAME FREQ. NO ADVISORY OF LIKE CALLSIGNS WAS ISSUED BY APCH. WE WERE TOLD TO EXPECT ILS 18R. LAST VECTOR FROM APCH WAS FOR US TO TURN L AND INTERCEPT ILS 18L. COMPANY ANSWERED FOR US. TCASII WARNING IMMEDIATELY SOUNDED 'CLB; CLB NOW!' WE PITCHED ACFT ABRUPTLY FROM LEVEL FLT TO ABOUT 4000 FPM. VISUALLY SAW ACR Y PASS 1/8 MI ON L AND ABOUT 100 FT BELOW US. ACR Y WAS IN A HARD R TURN IN AN OBVIOUS EVASIVE MANEUVER. WITHOUT TCASII; A MIDAIR COLLISION WOULD HAVE BEEN ALL BUT CERTAIN. SUPPLEMENTAL INFO FROM ACN 246628: WE WERE HDG 270 DEGS AT 4000 FT WHEN A 'TCASII WARNING' APPEARED 'TO CLB NOW.' WE IMMEDIATELY STARTED A MAX PWR CLB. THE OTHER ACFT APPEARED ON THE TCASII AS A RED SQUARE AND -01. WE VISUALLY SAW THE OTHER ACFT APPROX 100 FT BELOW US AND APPROX 1/4 MI AWAY. WE LEVELED OFF WHEN CLR OF TFC AND WERE VECTORED S FOR A VISUAL APCH TO RWY 18L.