Narrative:

I was hand flying the aircraft to our assigned cruising altitude of FL200. This was the altitude set in the altitude alert system. It had been set by the captain (who was handling ATC radio communications as the PNF) moments after acknowledging the altitude assignment from ATC (either ZHU or ZTL). The aircraft was at 19800' and climbing at approximately 500 FPM when ATC advised us that the mode C showed 19800' and instructed us to return to FL190. The captain then verified with the controller that FL190 was assigned and not FL200 as we believed. (But at one point the controller had a momentary doubt and asked, 'did I assign you FL230?') the captain looked at the flight plan which indicated we were filed at FL190 and stated we were now descending to FL190. This # was then entered in the altitude alert system. Upon leveling at FL190 the autoplt was engaged and the flight was conducted west/O further incident. I do not know where the error occurred. I can't recall what altitude assignment was stated by ATC. I can't recall what the captain's readback was. There was no distraction in the cockpit to divert attention. (There was no one else in the cockpit, we were not engaged in any notable conversation, and the flight was proceeding normally in VFR conditions.) I can only say that FL200 was set in the altitude alert system and that this never registered to me nor the captain as a discrepancy from ATC's clearance.

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Original NASA ASRS Text

Title: ALT BUST.

Narrative: I WAS HAND FLYING THE ACFT TO OUR ASSIGNED CRUISING ALT OF FL200. THIS WAS THE ALT SET IN THE ALT ALERT SYS. IT HAD BEEN SET BY THE CAPT (WHO WAS HANDLING ATC RADIO COMS AS THE PNF) MOMENTS AFTER ACKNOWLEDGING THE ALT ASSIGNMENT FROM ATC (EITHER ZHU OR ZTL). THE ACFT WAS AT 19800' AND CLBING AT APPROX 500 FPM WHEN ATC ADVISED US THAT THE MODE C SHOWED 19800' AND INSTRUCTED US TO RETURN TO FL190. THE CAPT THEN VERIFIED WITH THE CTLR THAT FL190 WAS ASSIGNED AND NOT FL200 AS WE BELIEVED. (BUT AT ONE POINT THE CTLR HAD A MOMENTARY DOUBT AND ASKED, 'DID I ASSIGN YOU FL230?') THE CAPT LOOKED AT THE FLT PLAN WHICH INDICATED WE WERE FILED AT FL190 AND STATED WE WERE NOW DSNDING TO FL190. THIS # WAS THEN ENTERED IN THE ALT ALERT SYS. UPON LEVELING AT FL190 THE AUTOPLT WAS ENGAGED AND THE FLT WAS CONDUCTED W/O FURTHER INCIDENT. I DO NOT KNOW WHERE THE ERROR OCCURRED. I CAN'T RECALL WHAT ALT ASSIGNMENT WAS STATED BY ATC. I CAN'T RECALL WHAT THE CAPT'S READBACK WAS. THERE WAS NO DISTR IN THE COCKPIT TO DIVERT ATTN. (THERE WAS NO ONE ELSE IN THE COCKPIT, WE WERE NOT ENGAGED IN ANY NOTABLE CONVERSATION, AND THE FLT WAS PROCEEDING NORMALLY IN VFR CONDITIONS.) I CAN ONLY SAY THAT FL200 WAS SET IN THE ALT ALERT SYS AND THAT THIS NEVER REGISTERED TO ME NOR THE CAPT AS A DISCREPANCY FROM ATC'S CLRNC.

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.