Narrative:

Talking to ZJX, we were on the buzzy 2 arrival into rdv and the controller instructed us to descend to and maintain 12000' and to arrive there before 35 mi southwest of sandhill. We read back the clearance and both the copilot and I wrote the clearance down (as I always do). Note: we both kept our scratch pads with the clearance written down. When I read the clearance back exactly: 'roger, cleared to maintain 1,2 thousand, 12000 35 mi southwest of sandhills,' the controller replied: 'roger.' we initiated a descent and as I left cruise I called leaving our cruise altitude to maintain 12000'. The controller sent us over to ZJX on 133.4. As we were passing FL210 I called in to center, 'jax, this is XXXX passing FL210 for 12000.' there was no reply then the controller replied (as we passed FL200), 'you were cleared to 210, maintain 210!' we immediately initiated a climb, catching our descent at about 19700', and leveled at 21000'. It is obvious the previous controller had intended to have us level at FL210 but reversed the numbers and instructed us to level at 12000', never acknowledging our reply to 12000' on 2 different occasions. I don't need to dwell on the drastic and tragic consequences this error could have caused, but ATC controllers must be more conscientious about reading back at least the altitude he clears an aircraft too, to make sure the pilots have understood his instructions and to make sure his instructions were correct.

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Original NASA ASRS Text

Title: ARTCC CLEARED ACFT TO 12000' BUT MEANT 21000'.

Narrative: TALKING TO ZJX, WE WERE ON THE BUZZY 2 ARR INTO RDV AND THE CTLR INSTRUCTED US TO DSND TO AND MAINTAIN 12000' AND TO ARRIVE THERE BEFORE 35 MI SW OF SANDHILL. WE READ BACK THE CLRNC AND BOTH THE COPLT AND I WROTE THE CLRNC DOWN (AS I ALWAYS DO). NOTE: WE BOTH KEPT OUR SCRATCH PADS WITH THE CLRNC WRITTEN DOWN. WHEN I READ THE CLRNC BACK EXACTLY: 'ROGER, CLRED TO MAINTAIN 1,2 THOUSAND, 12000 35 MI SW OF SANDHILLS,' THE CTLR REPLIED: 'ROGER.' WE INITIATED A DSCNT AND AS I LEFT CRUISE I CALLED LEAVING OUR CRUISE ALT TO MAINTAIN 12000'. THE CTLR SENT US OVER TO ZJX ON 133.4. AS WE WERE PASSING FL210 I CALLED IN TO CENTER, 'JAX, THIS IS XXXX PASSING FL210 FOR 12000.' THERE WAS NO REPLY THEN THE CTLR REPLIED (AS WE PASSED FL200), 'YOU WERE CLRED TO 210, MAINTAIN 210!' WE IMMEDIATELY INITIATED A CLB, CATCHING OUR DSCNT AT ABOUT 19700', AND LEVELED AT 21000'. IT IS OBVIOUS THE PREVIOUS CTLR HAD INTENDED TO HAVE US LEVEL AT FL210 BUT REVERSED THE NUMBERS AND INSTRUCTED US TO LEVEL AT 12000', NEVER ACKNOWLEDGING OUR REPLY TO 12000' ON 2 DIFFERENT OCCASIONS. I DON'T NEED TO DWELL ON THE DRASTIC AND TRAGIC CONSEQUENCES THIS ERROR COULD HAVE CAUSED, BUT ATC CTLRS MUST BE MORE CONSCIENTIOUS ABOUT READING BACK AT LEAST THE ALT HE CLRS AN ACFT TOO, TO MAKE SURE THE PLTS HAVE UNDERSTOOD HIS INSTRUCTIONS AND TO MAKE SURE HIS INSTRUCTIONS WERE CORRECT.

Data retrieved from NASA's ASRS site as of August 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.