E120 FLC INCORRECTLY INPUT ALT SELECTOR RESTR; THUS OVERSHOT ASSIGNED XING RESTR. FO DISAGREES WITH PIC'S RESPONSE TO ATC ALT QUERY.

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FLYING SCHEDULED COMMUTER AIRLINE SVC IN AN EMB120. THE CAPT WAS FLYING THE LEG. I WAS REVIEWING A CHART. WE WERE AT FL240 AND ISSUED A CLRNC TO DSND AND CROSS 30 DME NW OF SXC VOR AT AND MAINTAIN 11000 FT. WE WERE DSNDING AT 3000 FPM WHEN THE AUTOPLT FAILED TO CAPTURE ALT AT 11000 FT. THE CAPT ABRUPTLY LEVELED OFF; BUT BY THIS TIME WE WERE CLOSE TO 10000 FT. HE IMMEDIATELY BEGAN A CLB TO RETURN TO ASSIGNED ALT OF 11000 FT. ATC QUERIED US ABOUT OUR ALT. THE CAPT TOLD ME TO TELL HIM (ATC) WE WERE AT 11000 FT (BECAUSE OF HIS CORRECTION ALREADY BEING MADE). THE CTLR MADE SEVERAL COMMENTS ABOUT BEING ABLE TO GIVE US LOWER IF WE NEEDED IT. WE RETURNED QUICKLY TO 11000 FT AND NOTHING ELSE FOLLOWED. I DO FEEL IT IS NOT IN THE INTEREST OF SAFETY TO MISREPRESENT YOUR ALT. SUPPLEMENTAL INFO FROM ACN 389970: I WAS PNF AND MUST HAVE SET THE ALT ALERTER WITH A 'HALF DIGIT' BECAUSE WHILE DSNDING AT 3000 FPM WE WENT THROUGH 11000 FT AND THE AUTOPLT DID NOT CATCH THE ALT; BOTH FO'S HAD 'ALT SELECT' MISSING.