PIC OF AN LR35A PERFORMS AN ALT OVERSHOOT WHICH IS NOTED BY THE FO AND THE ZDC CTLR AFTER THE PIC HAD MISSED THE AMENDED CLRNC ALT CHANGE NEAR SBY; MD.

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THE CAPT WAS FLYING FROM THE L SEAT. WE CHKED IN WITH ZDC AND WERE GIVEN CLRNC TO CLB TO FL390. A MIN OR SO LATER WE WERE GIVEN AN AMENDED CLRNC TO CLB TO FL310. I READ BACK THE CLRNC AND SET THE AMENDED ALT INTO THE ALT PRE-SELECTOR. I THEN TURNED MY ATTN TO PROGRAMMING THE GPS THINKING THE CAPT HAD HEARD THE AMENDED CLRNC. A MIN OR SO WENT BY BEFORE I LOOKED UP TO SEE THE INSTS. AT THE SAME TIME I REALIZED WHAT ALT WE WERE AT (CLBING THROUGH 31700 FT); THE CAPT ASKED WHAT ALT WE WERE CLRED TO AND ZDC CALLED AND ASKED US OUR ALT. WE ENDED UP ALMOST 1000 FT ABOVE OUR ASSIGNED ALT OF 31000 FT BEFORE WE STARTED DOWN AGAIN. CONTRIBUTING FACTORS TO THE EVENT WAS 1) AN AMENDED CLRNC BY ZDC DURING A CLB. 2) MY LACK OF CREW COORD WITH THE CAPT TO MAKE CERTAIN THAT HE HEARD THE AMENDED CLRNC. 3) MY INATTENTION TO THE FLT INSTS DURING A CRITICAL PHASE OF FLT. 4) CAPT'S FAILURE TO HEAR THE AMENDED CLRNC. THIS TYPE OF SIT COULD HAVE BEEN PREVENTED BY BETTER COM/CREW COORD AND FOCUSING ON THE FLT INSTS DURING CLBS OR DSCNTS UNTIL LEVEL. SUPPLEMENTAL INFO FROM ACN 542217: DUE TO HIGH WORKLOAD AND MINDSET OF CLB TO CRUISE ALT (FL390) MISSED LEVELOFF AT FL310. FO ALSO MISSED CALLOUTS. SUPPLEMENTAL INFO FROM ACN 542204: ACFT CLBED THROUGH HIS ASSIGNED ALT OF FL310. WHEN I OBSERVED THIS I ASKED HIM TO SAY ALT. HE RESPONDED THAT HE HAD CLBED THROUGH HIS ASSIGNED ALT AND WAS DSNDING BACK TO FL310.