Narrative:

On the arrival into phoenix south of sacho intersection at FL330, I had the first officer request a lower altitude from center. (We were on a 260 degree heading for a vector around WX. There were a lot of thunderstorms in the area and on the published arrival. Also the frequency was very congested.) the controller immediately said 'maintain 260 on the heading descend to 12000'. We didn't make out the complete call sign, but the first officer read back the clearance with our call sign. I started descending. Out of approximately 32000 ft the controller called us and we were told to climb immediately to FL330. When on the ground I called the supervisor and he said we were on the tape reading back the clearance with our call sign, but the clearance had been meant for an air carrier Y flight and the controller had not heard our first call (for a lower altitude). He also hadn't picked up our clearance readback probably due to his busy workload. I believe that there were at least 3 factors that contributed to this altitude mixup. 1) extensive deviations (radar vectors) were occurring due to thunderstorms on the STAR increasing the controller's workload. 2) the radio frequency was very congested and there was a lot of 'covered transmissions' (blocked calls) adding to everyone's workload and confusion. 3) our flight path profile was showing over 5000 ft high on the FMC and this caused me to start right down without doublechking for the call sign and leaving only our 'clearance readback call sign' for the safety net. I realize that when things are busy I'm going to confirm clrncs anyway if I have any questions, because busy controllers miss things too. Supplemental information from acn 187328: 'albuquerque center, company identification, request lower'. The immediate reply from center was 'maintain 260 degree heading, descend and maintain 12000'. I acknowledged 'out of 330 for 12000 on heading 260 degree, with identification'. Center did not reply.

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Original NASA ASRS Text

Title: ACR MLG ALT DEV EXCURSION FROM CLRNC ALT IN RESPONSE TO WRONG CALL SIGN.

Narrative: ON THE ARR INTO PHOENIX S OF SACHO INTXN AT FL330, I HAD THE FO REQUEST A LOWER ALT FROM CENTER. (WE WERE ON A 260 DEG HDG FOR A VECTOR AROUND WX. THERE WERE A LOT OF TSTMS IN THE AREA AND ON THE PUBLISHED ARR. ALSO THE FREQ WAS VERY CONGESTED.) THE CTLR IMMEDIATELY SAID 'MAINTAIN 260 ON THE HDG DSND TO 12000'. WE DIDN'T MAKE OUT THE COMPLETE CALL SIGN, BUT THE FO READ BACK THE CLRNC WITH OUR CALL SIGN. I STARTED DSNDING. OUT OF APPROX 32000 FT THE CTLR CALLED US AND WE WERE TOLD TO CLB IMMEDIATELY TO FL330. WHEN ON THE GND I CALLED THE SUPVR AND HE SAID WE WERE ON THE TAPE READING BACK THE CLRNC WITH OUR CALL SIGN, BUT THE CLRNC HAD BEEN MEANT FOR AN ACR Y FLT AND THE CTLR HAD NOT HEARD OUR FIRST CALL (FOR A LOWER ALT). HE ALSO HADN'T PICKED UP OUR CLRNC READBACK PROBABLY DUE TO HIS BUSY WORKLOAD. I BELIEVE THAT THERE WERE AT LEAST 3 FACTORS THAT CONTRIBUTED TO THIS ALT MIXUP. 1) EXTENSIVE DEVS (RADAR VECTORS) WERE OCCURRING DUE TO TSTMS ON THE STAR INCREASING THE CTLR'S WORKLOAD. 2) THE RADIO FREQ WAS VERY CONGESTED AND THERE WAS A LOT OF 'COVERED TRANSMISSIONS' (BLOCKED CALLS) ADDING TO EVERYONE'S WORKLOAD AND CONFUSION. 3) OUR FLT PATH PROFILE WAS SHOWING OVER 5000 FT HIGH ON THE FMC AND THIS CAUSED ME TO START RIGHT DOWN WITHOUT DOUBLECHKING FOR THE CALL SIGN AND LEAVING ONLY OUR 'CLRNC READBACK CALL SIGN' FOR THE SAFETY NET. I REALIZE THAT WHEN THINGS ARE BUSY I'M GOING TO CONFIRM CLRNCS ANYWAY IF I HAVE ANY QUESTIONS, BECAUSE BUSY CTLRS MISS THINGS TOO. SUPPLEMENTAL INFO FROM ACN 187328: 'ALBUQUERQUE CENTER, COMPANY ID, REQUEST LOWER'. THE IMMEDIATE REPLY FROM CENTER WAS 'MAINTAIN 260 DEG HDG, DSND AND MAINTAIN 12000'. I ACKNOWLEDGED 'OUT OF 330 FOR 12000 ON HDG 260 DEG, WITH ID'. CENTER DID NOT REPLY.

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.