Narrative:

On our descent into tucson, approach control (125.10) cleared us to 9000 ft on a heading of 180 degrees. The approach controller appeared to be busy with military traffic on UHF. On our descent to 9000 ft the controller changed our altitude to 13000 ft. When we were at 13300 ft and descending, we responded 'air carrier X cleared to 13000 ft.' the controller then said 'go ahead and maintain 12000 ft. We responded 'roger down to 12000 air carrier X.' we heard no response to that so we assumed the readback was correct. Descending through 12300 ft our TCASII called traffic at 11 O'clock beyond 6 mi. No altitude was presented on display due to the traffic's distance from us. We then noticed the traffic's altitude was 300 ft below us. I then started leveling at 12300 ft until we could identify traffic. Just about the same time approach called traffic for us at 10 O'clock and I believe 4 mi at 12000 ft. The captain responded 'if he's at 12000 ft why are we cleared to 12000 ft.' the controller responded, 'air carrier X you were cleared to 13000 ft.' I then pitched up and added power to return to 'assigned' altitude. Shortly after adding power and beginning my climb. TCASII gave an RA 'monitor vertical speed.' it showed a red arc on ivsi in all areas except 2000 FPM descent. Seeing this I responded by reducing power and initiating descent. Just then the TCASII gave an RA 'descend, descend.' I responded by lowering pitch to initiate descent. Just then the conflicting traffic popped out of a cloud into view. He was at 12 O'clock slightly below us in a left bank moving left to right. Estimated distance was 1/2 mi. We then called to approach 'air carrier X has traffic in sight.' approach then said maintain 8000 ft. We maintained visual separation from the fgt as he passed left to right in front of us. Looking back into the occurrence, I feel that the problem occurred when we were issued clearance to 12000 ft. The clearance was immediately after we acknowledged our clearance to 13000 ft. We thought the controller amended our altitude to 12000 ft because we were approaching 13000 ft at such a high rate of descent. I think the phrase 'go ahead and maintain 12000 ft' was not for us, but for the fgt the controller was working on UHF.

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Original NASA ASRS Text

Title: ACR PLT TAKES CLRNC MEANT FOR ANOTHER ACFT AND DSNDED TO OCCUPIED ALT RESULTING IN LTSS.

Narrative: ON OUR DSCNT INTO TUCSON, APCH CTL (125.10) CLRED US TO 9000 FT ON A HDG OF 180 DEGS. THE APCH CTLR APPEARED TO BE BUSY WITH MIL TFC ON UHF. ON OUR DSCNT TO 9000 FT THE CTLR CHANGED OUR ALT TO 13000 FT. WHEN WE WERE AT 13300 FT AND DSNDING, WE RESPONDED 'ACR X CLRED TO 13000 FT.' THE CTLR THEN SAID 'GO AHEAD AND MAINTAIN 12000 FT. WE RESPONDED 'ROGER DOWN TO 12000 ACR X.' WE HEARD NO RESPONSE TO THAT SO WE ASSUMED THE READBACK WAS CORRECT. DSNDING THROUGH 12300 FT OUR TCASII CALLED TFC AT 11 O'CLOCK BEYOND 6 MI. NO ALT WAS PRESENTED ON DISPLAY DUE TO THE TFC'S DISTANCE FROM US. WE THEN NOTICED THE TFC'S ALT WAS 300 FT BELOW US. I THEN STARTED LEVELING AT 12300 FT UNTIL WE COULD IDENT TFC. JUST ABOUT THE SAME TIME APCH CALLED TFC FOR US AT 10 O'CLOCK AND I BELIEVE 4 MI AT 12000 FT. THE CAPT RESPONDED 'IF HE'S AT 12000 FT WHY ARE WE CLRED TO 12000 FT.' THE CTLR RESPONDED, 'ACR X YOU WERE CLRED TO 13000 FT.' I THEN PITCHED UP AND ADDED PWR TO RETURN TO 'ASSIGNED' ALT. SHORTLY AFTER ADDING PWR AND BEGINNING MY CLB. TCASII GAVE AN RA 'MONITOR VERT SPD.' IT SHOWED A RED ARC ON IVSI IN ALL AREAS EXCEPT 2000 FPM DSCNT. SEEING THIS I RESPONDED BY REDUCING PWR AND INITIATING DSCNT. JUST THEN THE TCASII GAVE AN RA 'DSND, DSND.' I RESPONDED BY LOWERING PITCH TO INITIATE DSCNT. JUST THEN THE CONFLICTING TFC POPPED OUT OF A CLOUD INTO VIEW. HE WAS AT 12 O'CLOCK SLIGHTLY BELOW US IN A L BANK MOVING L TO R. ESTIMATED DISTANCE WAS 1/2 MI. WE THEN CALLED TO APCH 'ACR X HAS TFC IN SIGHT.' APCH THEN SAID MAINTAIN 8000 FT. WE MAINTAINED VISUAL SEPARATION FROM THE FGT AS HE PASSED L TO R IN FRONT OF US. LOOKING BACK INTO THE OCCURRENCE, I FEEL THAT THE PROB OCCURRED WHEN WE WERE ISSUED CLRNC TO 12000 FT. THE CLRNC WAS IMMEDIATELY AFTER WE ACKNOWLEDGED OUR CLRNC TO 13000 FT. WE THOUGHT THE CTLR AMENDED OUR ALT TO 12000 FT BECAUSE WE WERE APCHING 13000 FT AT SUCH A HIGH RATE OF DSCNT. I THINK THE PHRASE 'GO AHEAD AND MAINTAIN 12000 FT' WAS NOT FOR US, BUT FOR THE FGT THE CTLR WAS WORKING ON UHF.

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.