Narrative:

While descending to FL240 a speed reduction to 250 KTS was given by center. A short time later we were also given a clearance to 12000 ft. The 'cleared to' altitude was read back to center, and the first officer verified that I had set the correct altitude in the alerter and then he verbally confirmed the altitude with me. After approximately 2 mins of level flight at 12000 ft and just prior to 'spane' intersection on the 'spane two' arrival, center called to confirm our altitude. I reported level at 12000 ft. Center informed us that we had been cleared only to 16000 ft. I replied that when given our descent clearance I had read back 12000 ft. We were then handed off to approach control and the remainder of the flight was normal. Looking back, I think that this situation could have been avoided by xchking our 'cleared to' altitude with published crossing restr on the arrival. In our case, 12000 ft was not a published altitude on the arrival. This clue should have caused us to not descend below the highest published crossing restr until verifying our cleared to altitude. A contributing factor could have been the high workload on the controller and the potential for a communication breakdown.

Related reports:

Google
 

Original NASA ASRS Text

Title: MLG ACFT GIVEN CLRNC TO 16000 FT BUT FLC THOUGHT 12000 FT AND READ THAT BACK. ATC CTLR WAS VERY BUSY AND DIDN'T CATCH ERROR ON READBACK.

Narrative: WHILE DSNDING TO FL240 A SPD REDUCTION TO 250 KTS WAS GIVEN BY CTR. A SHORT TIME LATER WE WERE ALSO GIVEN A CLRNC TO 12000 FT. THE 'CLRED TO' ALT WAS READ BACK TO CTR, AND THE FO VERIFIED THAT I HAD SET THE CORRECT ALT IN THE ALERTER AND THEN HE VERBALLY CONFIRMED THE ALT WITH ME. AFTER APPROX 2 MINS OF LEVEL FLT AT 12000 FT AND JUST PRIOR TO 'SPANE' INTXN ON THE 'SPANE TWO' ARR, CTR CALLED TO CONFIRM OUR ALT. I RPTED LEVEL AT 12000 FT. CTR INFORMED US THAT WE HAD BEEN CLRED ONLY TO 16000 FT. I REPLIED THAT WHEN GIVEN OUR DSCNT CLRNC I HAD READ BACK 12000 FT. WE WERE THEN HANDED OFF TO APCH CTL AND THE REMAINDER OF THE FLT WAS NORMAL. LOOKING BACK, I THINK THAT THIS SIT COULD HAVE BEEN AVOIDED BY XCHKING OUR 'CLRED TO' ALT WITH PUBLISHED XING RESTR ON THE ARR. IN OUR CASE, 12000 FT WAS NOT A PUBLISHED ALT ON THE ARR. THIS CLUE SHOULD HAVE CAUSED US TO NOT DSND BELOW THE HIGHEST PUBLISHED XING RESTR UNTIL VERIFYING OUR CLRED TO ALT. A CONTRIBUTING FACTOR COULD HAVE BEEN THE HIGH WORKLOAD ON THE CTLR AND THE POTENTIAL FOR A COM BREAKDOWN.

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.