Narrative:

At 16000 ft en route to mlo, ZMA issued a climb clearance to FL210. We changed our altitude selector to '210,' adjusted our cabin pressure control to FL210 and initiated a climb profile to FL210. At FL206, ZMA stated that we were 600 ft high and asked our assigned altitude. We replied 'FL210.' ZMA advised us our assigned altitude was FL200 and to descend, which we did. My first officer and I were sure our original assigned altitude was FL210. We read it back. One pilot (the first officer) adjusted the altitude selector to FL210 and the captain (me) stated 'FL210 confirmed.' that fact and our FL210 pressurization adjustment made it obvious that we were 'sure' of our assigned altitude. My personal policy is that if either pilot is unsure, we re-query the controller as to the instruction. We were sure. I know that controllers are very busy at times. It would result in mass confusion if every flight questioned every clearance that didn't make sense to the pilot. So we only question the ones we're unsure of the meaning of. If it's safe, possible and clear, we do it. This just reinforces the need to be sure of what we hear, verify clrncs with the other pilot (when we have one), query controllers when clrncs are unclr and for controllers to listen to and be sure they understand readbacks from pilots in case all the previous efforts still don't work. Discipline in standardized communication is critical to professionalism.

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Original NASA ASRS Text

Title: BEING SURE OF THEIR ALT CLRNC AND SETTING THE ALERTER PER COMPANY PROTOCOL, A CREW QUESTIONS THE FACT THAT ATC IS NOW QUESTIONING THEIR ALT JUST BEFORE LEVELOFF AS BEING ABOVE THEIR CLRNC ALT.

Narrative: AT 16000 FT ENRTE TO MLO, ZMA ISSUED A CLB CLRNC TO FL210. WE CHANGED OUR ALT SELECTOR TO '210,' ADJUSTED OUR CABIN PRESSURE CTL TO FL210 AND INITIATED A CLB PROFILE TO FL210. AT FL206, ZMA STATED THAT WE WERE 600 FT HIGH AND ASKED OUR ASSIGNED ALT. WE REPLIED 'FL210.' ZMA ADVISED US OUR ASSIGNED ALT WAS FL200 AND TO DSND, WHICH WE DID. MY FO AND I WERE SURE OUR ORIGINAL ASSIGNED ALT WAS FL210. WE READ IT BACK. ONE PLT (THE FO) ADJUSTED THE ALT SELECTOR TO FL210 AND THE CAPT (ME) STATED 'FL210 CONFIRMED.' THAT FACT AND OUR FL210 PRESSURIZATION ADJUSTMENT MADE IT OBVIOUS THAT WE WERE 'SURE' OF OUR ASSIGNED ALT. MY PERSONAL POLICY IS THAT IF EITHER PLT IS UNSURE, WE RE-QUERY THE CTLR AS TO THE INSTRUCTION. WE WERE SURE. I KNOW THAT CTLRS ARE VERY BUSY AT TIMES. IT WOULD RESULT IN MASS CONFUSION IF EVERY FLT QUESTIONED EVERY CLRNC THAT DIDN'T MAKE SENSE TO THE PLT. SO WE ONLY QUESTION THE ONES WE'RE UNSURE OF THE MEANING OF. IF IT'S SAFE, POSSIBLE AND CLR, WE DO IT. THIS JUST REINFORCES THE NEED TO BE SURE OF WHAT WE HEAR, VERIFY CLRNCS WITH THE OTHER PLT (WHEN WE HAVE ONE), QUERY CTLRS WHEN CLRNCS ARE UNCLR AND FOR CTLRS TO LISTEN TO AND BE SURE THEY UNDERSTAND READBACKS FROM PLTS IN CASE ALL THE PREVIOUS EFFORTS STILL DON'T WORK. DISCIPLINE IN STANDARDIZED COM IS CRITICAL TO PROFESSIONALISM.

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.