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.

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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.