Narrative:

Flight on feb/xa/05 at approximately XA32Z at FL310; approximately 50 mi southwest of mlf en route to slc from las on approximately 020 degree heading. ZLA switched us to ZLC; we then received numerous calls for traffic above and below our flight level. We observed all visually and on TCASII. Shortly thereafter; we received an aural traffic TCASII advisory followed by a yellow alert showing traffic at 11 O'clock position descending through FL317. This was followed by an RA commanding a 1500 FPM descent. Aircraft was immediately taken off autoplt and autothrottles and we initiated a descent as commanded. The 'clear of conflict' came after the conflicting aircraft passed overhead and we leveled off at FL305. The first officer immediately called center when we initiated the RA-commanded descent. No immediate response was made by center. An air carrier Z aircraft was on the same track; slightly aft of our position at FL330. He also called out a climbing RA to center. We both inquired about the conflicting aircraft and were told it was air carrier Y working with ZLA en route from slc to las. We were working on 125.57 ZLC and requested a phone number to call and advised them of our intentions to file an near midair collision. When center acknowledged both of our RA calls; it was noted there was some warning horn in the backgnd on center radio transmission. The last call we received from center regarding this; they said something about air carrier Y having a TCASII problem. We spoke to the safety coordinator with pilot union in ZZZ and slc chief pilot in between flts and passed along all information. In the morning; we determined we needed to call ZLA; who was working the air carrier Y flight. They admitted to controller error and they took the information to file the near midair collision. We were told that the air carrier Y aircraft was given a clearance to descend to FL290 with pilot's discretion to FL240. This was the error made by the ZLA controller when he was handed the air carrier Y aircraft form ZLC. ZLC was unaware of this clearance while handling our flight on their frequency. We were on 2 different frequencys in the same airspace. It is my understanding air carrier Y stopped the descent at FL315 and climbed back to FL320; thus clearing the conflict but setting off the momentary RA on air carrier Z while initiating the climb; even though he did not climb into their airspace. What if air carrier Y was making a more rapid descent and their TCASII was inoperative (not required for rvsm) and we had traffic at FL300 below us? No room for error and we might have conflicts with that traffic as well.

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Original NASA ASRS Text

Title: B757 FLT CREW EXPERIENCED TCASII RA AT FL310 INVOLVING 3 ACFT ON BOTH ZLC AND ZLA FREQS.

Narrative: FLT ON FEB/XA/05 AT APPROX XA32Z AT FL310; APPROX 50 MI SW OF MLF ENRTE TO SLC FROM LAS ON APPROX 020 DEG HDG. ZLA SWITCHED US TO ZLC; WE THEN RECEIVED NUMEROUS CALLS FOR TFC ABOVE AND BELOW OUR FLT LEVEL. WE OBSERVED ALL VISUALLY AND ON TCASII. SHORTLY THEREAFTER; WE RECEIVED AN AURAL TFC TCASII ADVISORY FOLLOWED BY A YELLOW ALERT SHOWING TFC AT 11 O'CLOCK POS DSNDING THROUGH FL317. THIS WAS FOLLOWED BY AN RA COMMANDING A 1500 FPM DSCNT. ACFT WAS IMMEDIATELY TAKEN OFF AUTOPLT AND AUTOTHROTTLES AND WE INITIATED A DSCNT AS COMMANDED. THE 'CLR OF CONFLICT' CAME AFTER THE CONFLICTING ACFT PASSED OVERHEAD AND WE LEVELED OFF AT FL305. THE FO IMMEDIATELY CALLED CTR WHEN WE INITIATED THE RA-COMMANDED DSCNT. NO IMMEDIATE RESPONSE WAS MADE BY CTR. AN ACR Z ACFT WAS ON THE SAME TRACK; SLIGHTLY AFT OF OUR POS AT FL330. HE ALSO CALLED OUT A CLBING RA TO CTR. WE BOTH INQUIRED ABOUT THE CONFLICTING ACFT AND WERE TOLD IT WAS ACR Y WORKING WITH ZLA ENRTE FROM SLC TO LAS. WE WERE WORKING ON 125.57 ZLC AND REQUESTED A PHONE NUMBER TO CALL AND ADVISED THEM OF OUR INTENTIONS TO FILE AN NMAC. WHEN CTR ACKNOWLEDGED BOTH OF OUR RA CALLS; IT WAS NOTED THERE WAS SOME WARNING HORN IN THE BACKGND ON CTR RADIO XMISSION. THE LAST CALL WE RECEIVED FROM CTR REGARDING THIS; THEY SAID SOMETHING ABOUT ACR Y HAVING A TCASII PROB. WE SPOKE TO THE SAFETY COORDINATOR WITH PLT UNION IN ZZZ AND SLC CHIEF PLT IN BTWN FLTS AND PASSED ALONG ALL INFO. IN THE MORNING; WE DETERMINED WE NEEDED TO CALL ZLA; WHO WAS WORKING THE ACR Y FLT. THEY ADMITTED TO CTLR ERROR AND THEY TOOK THE INFO TO FILE THE NMAC. WE WERE TOLD THAT THE ACR Y ACFT WAS GIVEN A CLRNC TO DSND TO FL290 WITH PLT'S DISCRETION TO FL240. THIS WAS THE ERROR MADE BY THE ZLA CTLR WHEN HE WAS HANDED THE ACR Y ACFT FORM ZLC. ZLC WAS UNAWARE OF THIS CLRNC WHILE HANDLING OUR FLT ON THEIR FREQ. WE WERE ON 2 DIFFERENT FREQS IN THE SAME AIRSPACE. IT IS MY UNDERSTANDING ACR Y STOPPED THE DSCNT AT FL315 AND CLBED BACK TO FL320; THUS CLRING THE CONFLICT BUT SETTING OFF THE MOMENTARY RA ON ACR Z WHILE INITIATING THE CLB; EVEN THOUGH HE DID NOT CLB INTO THEIR AIRSPACE. WHAT IF ACR Y WAS MAKING A MORE RAPID DSCNT AND THEIR TCASII WAS INOP (NOT REQUIRED FOR RVSM) AND WE HAD TFC AT FL300 BELOW US? NO ROOM FOR ERROR AND WE MIGHT HAVE CONFLICTS WITH THAT TFC AS WELL.

Data retrieved from NASA's ASRS site as of January 2009 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.