Narrative:

While flying direct to omn, we received a clearance that we understood to be 'cleared to cross 90 mi north of omn at FL210.' the first officer read back 'roger, cleared to cross 90 mi north of omn at FL210.' I set FL210 in the altitude window, and the first officer verified FL210. We began the descent to make the crossing restr. Just prior to leveling off, the controller asked us to verify altitude, and the first officer said 'leveling at FL210.' the controller said 'FL210? -- You were cleared to FL310.' the first officer responded, 'sir, we understood FL210 and read back FL210, do you need us to climb?' the controller, after a pause, said 'no, maintain FL210.' there were no traffic conflicts and no TCASII advisories. We also had a jumpseat rider, another captain, and he later told us he thought he heard the clearance to be FL210. Just as soon as we acknowledged the original clearance to FL210, another aircraft made an immediate radio call, which could have distraction the controller's attention from acknowledging our readback. We were all fortunate there was no conflict during this incident. Possible corrective measures could be more attentiveness from both ends. If something doesn't seem exactly right, it should be questioned. To me, it seemed a little early to descend that early to that altitude. Even though our acknowledgement was not questioned by the controller, if I had questioned the clearance, it maybe could have been avoided.

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Original NASA ASRS Text

Title: AN A319 FLT CREW AND A ZJX CTLR GET CONFUSED AS TO WHAT ALT THE ACFT WAS CLRED TO DSND TO.

Narrative: WHILE FLYING DIRECT TO OMN, WE RECEIVED A CLRNC THAT WE UNDERSTOOD TO BE 'CLRED TO CROSS 90 MI N OF OMN AT FL210.' THE FO READ BACK 'ROGER, CLRED TO CROSS 90 MI N OF OMN AT FL210.' I SET FL210 IN THE ALT WINDOW, AND THE FO VERIFIED FL210. WE BEGAN THE DSCNT TO MAKE THE XING RESTR. JUST PRIOR TO LEVELING OFF, THE CTLR ASKED US TO VERIFY ALT, AND THE FO SAID 'LEVELING AT FL210.' THE CTLR SAID 'FL210? -- YOU WERE CLRED TO FL310.' THE FO RESPONDED, 'SIR, WE UNDERSTOOD FL210 AND READ BACK FL210, DO YOU NEED US TO CLB?' THE CTLR, AFTER A PAUSE, SAID 'NO, MAINTAIN FL210.' THERE WERE NO TFC CONFLICTS AND NO TCASII ADVISORIES. WE ALSO HAD A JUMPSEAT RIDER, ANOTHER CAPT, AND HE LATER TOLD US HE THOUGHT HE HEARD THE CLRNC TO BE FL210. JUST AS SOON AS WE ACKNOWLEDGED THE ORIGINAL CLRNC TO FL210, ANOTHER ACFT MADE AN IMMEDIATE RADIO CALL, WHICH COULD HAVE DISTR THE CTLR'S ATTN FROM ACKNOWLEDGING OUR READBACK. WE WERE ALL FORTUNATE THERE WAS NO CONFLICT DURING THIS INCIDENT. POSSIBLE CORRECTIVE MEASURES COULD BE MORE ATTENTIVENESS FROM BOTH ENDS. IF SOMETHING DOESN'T SEEM EXACTLY RIGHT, IT SHOULD BE QUESTIONED. TO ME, IT SEEMED A LITTLE EARLY TO DSND THAT EARLY TO THAT ALT. EVEN THOUGH OUR ACKNOWLEDGEMENT WAS NOT QUESTIONED BY THE CTLR, IF I HAD QUESTIONED THE CLRNC, IT MAYBE COULD HAVE BEEN AVOIDED.

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.