Narrative:

Air carrier X cleared civet arrival to cross arnes at 11000 ft, then cleared ILS runway 25L. Were IMC from approximately 10000 ft to 4000 ft AGL. Aircraft slowed from 250 KTS to 210 KTS to 190 KTS to 180 KTS at ATC request. Difficult to slow and maintain GS with tailwind. Called tower at OM in VMC, informed them of wind, got clearance to land on runway 25L. Observed no traffic in our area, TCASII was on 10 mi range and looking below. Some targets in vicinity of airport observed on TCASII, but none were a factor. At approximately 1300 ft AGL, a TA 'traffic, traffic' was heard. I checked the TCASII/vsi and saw a yellow DOT overlapping our 6 O'clock position with a plus 2 annunciated. First officer and I checked area for traffic, observed none. No call from ATC, we assumed TCASII had malfunctioned. We received a second TA from 4:30 position, plus 2, and promptly scanned the area again, but becoming suspicious and unsure of a course of action. Then the DOT on TCASII turned red at 3 O'clock, showing plus 1, and first officer called 'traffic in sight,' and I saw a twin turboprop pass 50 ft above and 100 ft right and moving slowly right. First officer called tower, advised RA with aircraft on right and tower replied 'he's visual to runway 25R.' we slowed, moved left, realigned with runway 25L from slightly left of course and landed. The other aircraft, air carrier Y, passed us and landed on runway 25R. We don't know where he came from, were not informed of his presence, purpose, or clearance. I think he was cleared visual to runway 25R and probably never saw us in his blind spot or he would not have passed us. ATC procedures must be reviewed or Y needs more safety training.

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Original NASA ASRS Text

Title: MULTIPLE RWY OP PARALLEL RWYS ACR X TCASII TA HAD NMAC WITH ACR Y FOR PARALLEL RWYS. VISUAL SEPARATION IN USE.

Narrative: ACR X CLRED CIVET ARR TO CROSS ARNES AT 11000 FT, THEN CLRED ILS RWY 25L. WERE IMC FROM APPROX 10000 FT TO 4000 FT AGL. ACFT SLOWED FROM 250 KTS TO 210 KTS TO 190 KTS TO 180 KTS AT ATC REQUEST. DIFFICULT TO SLOW AND MAINTAIN GS WITH TAILWIND. CALLED TWR AT OM IN VMC, INFORMED THEM OF WIND, GOT CLRNC TO LAND ON RWY 25L. OBSERVED NO TFC IN OUR AREA, TCASII WAS ON 10 MI RANGE AND LOOKING BELOW. SOME TARGETS IN VICINITY OF ARPT OBSERVED ON TCASII, BUT NONE WERE A FACTOR. AT APPROX 1300 FT AGL, A TA 'TFC, TFC' WAS HEARD. I CHKED THE TCASII/VSI AND SAW A YELLOW DOT OVERLAPPING OUR 6 O'CLOCK POS WITH A PLUS 2 ANNUNCIATED. FO AND I CHKED AREA FOR TFC, OBSERVED NONE. NO CALL FROM ATC, WE ASSUMED TCASII HAD MALFUNCTIONED. WE RECEIVED A SECOND TA FROM 4:30 POS, PLUS 2, AND PROMPTLY SCANNED THE AREA AGAIN, BUT BECOMING SUSPICIOUS AND UNSURE OF A COURSE OF ACTION. THEN THE DOT ON TCASII TURNED RED AT 3 O'CLOCK, SHOWING PLUS 1, AND FO CALLED 'TFC IN SIGHT,' AND I SAW A TWIN TURBOPROP PASS 50 FT ABOVE AND 100 FT R AND MOVING SLOWLY R. FO CALLED TWR, ADVISED RA WITH ACFT ON R AND TWR REPLIED 'HE'S VISUAL TO RWY 25R.' WE SLOWED, MOVED L, REALIGNED WITH RWY 25L FROM SLIGHTLY L OF COURSE AND LANDED. THE OTHER ACFT, ACR Y, PASSED US AND LANDED ON RWY 25R. WE DON'T KNOW WHERE HE CAME FROM, WERE NOT INFORMED OF HIS PRESENCE, PURPOSE, OR CLRNC. I THINK HE WAS CLRED VISUAL TO RWY 25R AND PROBABLY NEVER SAW US IN HIS BLIND SPOT OR HE WOULD NOT HAVE PASSED US. ATC PROCS MUST BE REVIEWED OR Y NEEDS MORE SAFETY TRAINING.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.