Narrative:

I was the copilot on this flight. My captain was discussing an issue with the lead flight attendant, so I was responsible for flying the aircraft and communicating with ATC. ATC cleared us to descend to FL270. I heard 'FL270,' read back 'FL270,' but set 26000 ft in the altitude window, thinking I had set 27000 ft. I initiated the descent via autoplt. During the descent my captain concluded her discussion with the flight attendant, and I told her we had been cleared to FL260. Upon leveling at FL260, I noticed ATC had just cleared another aircraft to descend to FL270. I queried ATC about our altitude. The controller responded that 'FL270 was assigned, descend now to FL240 and expedite through FL250.' I disconnected the autoplt and extended the speed brakes to expedite the descent. The controller reiterated 'be out of FL250 as rapidly as possible' or something to that effect. I reported being below FL250. After leveling at FL240, we were then handed off to the next sector, with no apparent conflict generated by our altitude deviation. I believe this was a case of me seeing what I wanted to see in the altitude window, and then, convinced I had properly set the altitude, thinking FL260 was the assigned altitude. Fatigue may have played a small role as it had been a busy flight with an equipment malfunction, thunderstorm avoidance, and a high workload international departure. I will be more diligent in the future when as both PF and communicating with ATC, I am the only safeguard in complying with ATC clrncs. Supplemental information from acn 404400: contributing factors: since the departure out of mexico city, the workload had been high due to radar failure, an increasing temperature on a pack that had been a problem on the previous flight and cleared by mex maintenance, inability to talk to company due to intermittent ACARS and no working commercial radio frequency until closer to houston. In an attempt to remedy these problems I had asked the first officer to use the autoplt and work the radios on 2 or 3 occasions. This coordination seemed to work well and things went smooth. I believe the first officer saw me talking to the flight attendant and when I missed the call, assumed it was ok to answer ATC and descend. However, without my verification of altitude, our situation caused a questionable altitude deviation.

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Original NASA ASRS Text

Title: EA32 ALT BUST. CREW WAS DISTRACTED WHEN THE CAPT WAS DISCUSSING A MAINT PROB WITH THE CABIN ATTENDANT. THE FO SET A WRONG ALT IN THE ALT WINDOW, AND THE AUTOPLT DSNDED TO THAT ALT.

Narrative: I WAS THE COPLT ON THIS FLT. MY CAPT WAS DISCUSSING AN ISSUE WITH THE LEAD FLT ATTENDANT, SO I WAS RESPONSIBLE FOR FLYING THE ACFT AND COMMUNICATING WITH ATC. ATC CLRED US TO DSND TO FL270. I HEARD 'FL270,' READ BACK 'FL270,' BUT SET 26000 FT IN THE ALT WINDOW, THINKING I HAD SET 27000 FT. I INITIATED THE DSCNT VIA AUTOPLT. DURING THE DSCNT MY CAPT CONCLUDED HER DISCUSSION WITH THE FLT ATTENDANT, AND I TOLD HER WE HAD BEEN CLRED TO FL260. UPON LEVELING AT FL260, I NOTICED ATC HAD JUST CLRED ANOTHER ACFT TO DSND TO FL270. I QUERIED ATC ABOUT OUR ALT. THE CTLR RESPONDED THAT 'FL270 WAS ASSIGNED, DSND NOW TO FL240 AND EXPEDITE THROUGH FL250.' I DISCONNECTED THE AUTOPLT AND EXTENDED THE SPD BRAKES TO EXPEDITE THE DSCNT. THE CTLR REITERATED 'BE OUT OF FL250 AS RAPIDLY AS POSSIBLE' OR SOMETHING TO THAT EFFECT. I RPTED BEING BELOW FL250. AFTER LEVELING AT FL240, WE WERE THEN HANDED OFF TO THE NEXT SECTOR, WITH NO APPARENT CONFLICT GENERATED BY OUR ALTDEV. I BELIEVE THIS WAS A CASE OF ME SEEING WHAT I WANTED TO SEE IN THE ALT WINDOW, AND THEN, CONVINCED I HAD PROPERLY SET THE ALT, THINKING FL260 WAS THE ASSIGNED ALT. FATIGUE MAY HAVE PLAYED A SMALL ROLE AS IT HAD BEEN A BUSY FLT WITH AN EQUIP MALFUNCTION, TSTM AVOIDANCE, AND A HIGH WORKLOAD INTL DEP. I WILL BE MORE DILIGENT IN THE FUTURE WHEN AS BOTH PF AND COMMUNICATING WITH ATC, I AM THE ONLY SAFEGUARD IN COMPLYING WITH ATC CLRNCS. SUPPLEMENTAL INFO FROM ACN 404400: CONTRIBUTING FACTORS: SINCE THE DEP OUT OF MEXICO CITY, THE WORKLOAD HAD BEEN HIGH DUE TO RADAR FAILURE, AN INCREASING TEMP ON A PACK THAT HAD BEEN A PROB ON THE PREVIOUS FLT AND CLRED BY MEX MAINT, INABILITY TO TALK TO COMPANY DUE TO INTERMITTENT ACARS AND NO WORKING COMMERCIAL RADIO FREQ UNTIL CLOSER TO HOUSTON. IN AN ATTEMPT TO REMEDY THESE PROBS I HAD ASKED THE FO TO USE THE AUTOPLT AND WORK THE RADIOS ON 2 OR 3 OCCASIONS. THIS COORD SEEMED TO WORK WELL AND THINGS WENT SMOOTH. I BELIEVE THE FO SAW ME TALKING TO THE FLT ATTENDANT AND WHEN I MISSED THE CALL, ASSUMED IT WAS OK TO ANSWER ATC AND DSND. HOWEVER, WITHOUT MY VERIFICATION OF ALT, OUR SIT CAUSED A QUESTIONABLE ALTDEV.

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.