Narrative:

Flight was cleared to descend and maintain 10000' MSL, and it was heard and read back as a clearance to 10000' by the first officer. The altitude alert was set and armed to 10000', and as I was later leveling off at 10000', the controller said 'climb to 11000'.' as we had just leveled at 10000', it alarmed me and I confirmed aloud to the controller 'weren't we cleared to 10000'?' he replied we were only cleared to 11000'. I immediately climbed back to 11000' and leveled off. In discussion, all 3 crew members agreed that we had understood the clearance to 10000', and it was read back as 'cleared to 10000'.' this disturbs me in that there was holding commencing at plant intersection, and there could have been a traffic conflict of a serious nature. We were in bright sunshine above the clouds at the time, but it is often difficult to see other aircraft in a holding pattern. I'm not sure how this problem could be prevented from occurring again. It is a chronic problem in modern aviation--misunderstood clrncs when they are read back incorrectly and not caught by ATC and clrncs read back correctly, but misunderstood by the cockpit crew. The only solution I can apply to myself is to increase awareness even more whenever clrncs are received and to have an assurance all cockpit crew members understand them. I also want ATC to be aware what the crew has in mind performing after a clearance is received. I intend to brief my crew in a clear and concise manner about the redundant importance of reading back clrncs clearly and not to rush or talk too fast when reading back a clearance. Supplemental information from acn 134155: ATC was obviously taxed by the need to hold arrival traffic into chicago and we the cockpit were rethinking a hold situation which requires a deal of intra-cockpit communication.

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Original NASA ASRS Text

Title: ACR LGT ALT DEVIATION OVERSHOT DURING DESCENT, 10000'-11000' MISUNDERSTANDING.

Narrative: FLT WAS CLRED TO DSND AND MAINTAIN 10000' MSL, AND IT WAS HEARD AND READ BACK AS A CLRNC TO 10000' BY THE F/O. THE ALT ALERT WAS SET AND ARMED TO 10000', AND AS I WAS LATER LEVELING OFF AT 10000', THE CTLR SAID 'CLB TO 11000'.' AS WE HAD JUST LEVELED AT 10000', IT ALARMED ME AND I CONFIRMED ALOUD TO THE CTLR 'WEREN'T WE CLRED TO 10000'?' HE REPLIED WE WERE ONLY CLRED TO 11000'. I IMMEDIATELY CLBED BACK TO 11000' AND LEVELED OFF. IN DISCUSSION, ALL 3 CREW MEMBERS AGREED THAT WE HAD UNDERSTOOD THE CLRNC TO 10000', AND IT WAS READ BACK AS 'CLRED TO 10000'.' THIS DISTURBS ME IN THAT THERE WAS HOLDING COMMENCING AT PLANT INTXN, AND THERE COULD HAVE BEEN A TFC CONFLICT OF A SERIOUS NATURE. WE WERE IN BRIGHT SUNSHINE ABOVE THE CLOUDS AT THE TIME, BUT IT IS OFTEN DIFFICULT TO SEE OTHER ACFT IN A HOLDING PATTERN. I'M NOT SURE HOW THIS PROB COULD BE PREVENTED FROM OCCURRING AGAIN. IT IS A CHRONIC PROB IN MODERN AVIATION--MISUNDERSTOOD CLRNCS WHEN THEY ARE READ BACK INCORRECTLY AND NOT CAUGHT BY ATC AND CLRNCS READ BACK CORRECTLY, BUT MISUNDERSTOOD BY THE COCKPIT CREW. THE ONLY SOLUTION I CAN APPLY TO MYSELF IS TO INCREASE AWARENESS EVEN MORE WHENEVER CLRNCS ARE RECEIVED AND TO HAVE AN ASSURANCE ALL COCKPIT CREW MEMBERS UNDERSTAND THEM. I ALSO WANT ATC TO BE AWARE WHAT THE CREW HAS IN MIND PERFORMING AFTER A CLRNC IS RECEIVED. I INTEND TO BRIEF MY CREW IN A CLEAR AND CONCISE MANNER ABOUT THE REDUNDANT IMPORTANCE OF READING BACK CLRNCS CLEARLY AND NOT TO RUSH OR TALK TOO FAST WHEN READING BACK A CLRNC. SUPPLEMENTAL INFO FROM ACN 134155: ATC WAS OBVIOUSLY TAXED BY THE NEED TO HOLD ARR TFC INTO CHICAGO AND WE THE COCKPIT WERE RETHINKING A HOLD SITUATION WHICH REQUIRES A DEAL OF INTRA-COCKPIT COM.

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.