ACR MLG ACFT UNDERSHOT DSCNT XING ALT DUE TO THE FO MAKING A FLT COMPUTER ENTRY ERROR.

Narrative

WE WERE FLYING ATL TO MKE WHEN APPROX 100 NM S OF BRAVE INTXN ON DIRECT RTE TO BRAVE; CHICAGO CLRED US TO CROSS 50 NM S OF BRAVE AT FL240. I READ BACK CLRNC AND FO (PF) SET ALT IN REMINDER WINDOW AND MADE ENTRY INTO FMS TO CREATE DSCNT PROFILE. DURING THIS TIME I WAS GETTING ARR ATIS FOR MKE WHILE OBSERVING PROPER ALT HAD BEEN SET BY FO AND THAT A POINT HAD BEEN CREATED BTWN OUR PRESENT POS AND BRAVE. A FEW MINS HAD PASSED WHEN CHICAGO CALLED AND ASKED OUR DME S OF BRAVE. I ADDED OUR DISTANCE TO CREATED FMS WAYPOINT PLUS DISTANCE TO BRAVE AND RPTED IT TO BE 56 MI; IMMEDIATELY REALIZING THAT THE WAYPOINT HAD BEEN ENTERED INCORRECTLY; WE WERE STILL AT FL350. CHICAGO IMMEDIATELY CANCELLED XING RESTRICTION; CLRED US TO FL240; AND WE BEGAN OUR DSCNT. EXAMINATION SHOWED THAT THE FO HAD INADVERTENTLY TYPED THE DME S OF BRAVE TO CROSS; AS 24 NM INSTEAD OF 50 NM; HE HAD USED THE FLT LEVEL AS THE DME BY MISTAKE EVEN THOUGH WE HAD BOTH VERBALIZED THE CLRNC. NORMALLY I ALWAYS XCHK ALL FMS ENTRIES. HOWEVER; THIS TIME I BECAME DISTRACTED BY GETTING THE MKE ATIS RIGHT AFTER RECEIVING THE INITIAL CLRNC. THEN WE BOTH BECAME INVOLVED IN APCH PLANS SINCE THE WIND WAS OUT OF THE S AT 10-13 KTS AND OUR EARLIER PREPARATIONS WERE FOR A 19R ARR. HOWEVER; THE ARPT WAS USING 25L WITH A LOC APCH REQUIRING US TO NOW GET PREPARED FOR IT AND RECONFIGURE OUR NAV EQUIP. THESE DISTRS OBVIOUSLY INTERFERED WITH MY NORMAL FMS XCHKS UNTIL IT WAS TOO LATE. THE OBVIOUS SOLUTION TO THIS SITUATION WOULD HAVE BEEN MY CHK OF THE FMS INPUT; WHICH I FAILED TO DO.