ACFT MISSES XING ALT BY 4000 FT.

Narrative

ENRTE TO PHL FROM FLL AT FL240; CLRNC WAS TO CROSS 30 NM S OF SEA ISLE (SIE) AT 15000 FT. I ENTERED THAT POINT INTO THE FMC; SET THE ALT ALERTER WITH CONCURRENCE OF THE FO; AND STARTED A 1000 FPM DSCNT USING 'VERT SPD.' THEN REFING THE 'DSCNT PAGE' AND NOTING A REQUIRED RATE OF 1250 FPM; I SET THE VERT SPD TO 1300 FPM TO MAKE THE RESTR. WE WERE BOTH SET UP IN NAV MODE; WITH NO SIE RAW DATA DISPLAYED. THE LEAD FLT ATTENDANT THEN CALLED THE FO WITH A CABIN DISCREPANCY NEEDING MAINT UPON ARR IN PHL; WHILE I MONITORED ATC. I THEN GOT OUT THE LOGBOOK TO RECORD THE ITEM. A MIN OR SO LATER; ATC ASKED IF WE HAD BEEN GIVEN A XING RESTR. UPON CHKING THE FMC; WE HAD ALREADY PASSED THE XING POINT AND WERE ABOUT 25 NM S OF SIE PASSING FL190. I THEN REALIZED I HAD INADVERTENTLY INSERTED THE 15000 FT AT SIE; RATHER THAN AT THE 30 S POINT I HAD CREATED. THIS OCCURRENCE POINTS OUT THE NEED FOR BOTH PLTS TO XCHK AND CONFIRM ALL FMC ENTRIES; AS WELL AS THE NEED FOR A RAW DATA BACKUP FOR ALL XING RESTRS (ESPECIALLY IMPORTANT FOR NON EFIS EQUIPPED ACFT SUCH AS OURS; WHERE THE 'BIG PICTURE' IS NOT SO READILY APPARENT). DURING DISTRS FROM THE CABIN; IT IS IMPERATIVE THAT 1 PLT CONTINUE TO CONCENTRATE SOLELY ON NAVING THE ACFT.