AFTER RECEIVING AN ALT XING RESTR; THE PF INADVERTENTLY LEVELED 1000 FT ABOVE THE ASSIGNED ALT. THE PNF WAS GETTING THE ATIS AND MAKING A PA AND FAILED TO NOTICE THE ALTDEV. ARTCC RADAR CTLR INTERVENED.

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WE WERE CLRED BY ZAU TO CROSS PIVOT AT 10000 FT WHICH I SET AND PF ACKNOWLEDGED IN OUR ALT ALERT WINDOW. PF WAS DSNDING. I WAS OFF FREQ MOMENTARILY GETTING ATIS AND MAKING PA ANNOUNCEMENT. WHEN I GOT BACK IN LOOP; EVERYTHING SEEMED STABILIZED (LEVEL AND ON SPD). JUST THEN; ZAU CALLED US AND SAID MAINTAIN 10000 FT. I CHKED AND WE WERE LEVEL AT 11000 FT JUST A COUPLE MI W OF PIVOT (OUR XING POINT). PF SAID SHE DIDN'T REALIZE SHE HAD LEVELED OFF AT 11000 FT AND WE IMMEDIATELY DSNDED TO 10000 FT. UPON COMPLETION OF THE FLT WE HAD A THOROUGH DISCUSSION ABOUT HOW THIS HAPPENED AND WHAT SOP BREAKDOWNS (IF ANY) WOULD HAVE PREVENTED IT. OBVIOUSLY PF DID NOT GET A 1000 FT TO GO CALL FROM ME (I WAS OFF AND BUSY); OR FROM THE ACFT SYS WHICH SHOULD HAVE RAISED A FLAG ABOUT LEVELING OFF AT 11000 FT. SHE ALSO SAID THAT SHE WAS DISTRACTED WITH THE AIRSPD TRYING TO MAINTAIN 320 KTS. WE DON'T BELIEVE THIS CAUSED ANY CONFLICT; OR WAS A PROB WITH ZAU; BUT WE KNOW HOW IT OCCURRED AND HOW TO BE ALERT TO NOT ALLOWING SUCH OCCURRENCES.