MD88 CREW DEVIATES FROM CLRED COURSE IN ZOB AIRSPACE.

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ON CLBOUT FROM PITTSBURGH; I WAS GIVEN A HDG TO INTERCEPT THE AGC 221 DEG RADIAL TO BURGS INTXN; THEN AS FILED. ANTICIPATING THIS CLRNC; I HAD LOADED IT INTO THE FMS. WHEN CLRED TO INTERCEPT; I WAS HAND FLYING THE ACFT; SO I HAD THE CAPT SELECT THE INTERCEPT IN THE FMS. I WAS WATCHING THE FMS XTRACK TO SEE THE INTERCEPT. AS WE GOT CLOSE TO THE INTERCEPT ON THE MAP DISPLAY; I SWITCHED TO ARC ON MY DISPLAY TO XCHK THE RADIAL FROM AGC (WHICH I HAD TUNED IN). I IMMEDIATELY NOTICED WE WERE PAST THE RADIAL AND CONFIRMED IT ON MY RMI. I TURNED TO PARALLEL COURSE AND ASKED THE CAPT ABOUT THE FMS. WE WERE ON THE 212 DEG RADIAL WHEN INDIANAPOLIS ASKED ABOUT OUR CLRNC. WE TOLD HIM WE WERE CORRECTING BACK TO THE 221 DEG RADIAL. HE SAID JUST TO PROCEED TO HVQ VOR (CHARLESTON) AND THEN AS FILED. AFTER DISCUSSING THIS WITH THE CAPT; WE FIGURED HE MUST HAVE RELOADED THE FMS INCORRECTLY WHEN WE RECEIVED THE CLRNC. I DID NOT REALIZE HE HAD CHANGED WHAT I HAD LOADED. I SHOULD HAVE CHKED THE FMS MORE CLOSELY AND MONITORED MY RMI MORE CLOSELY.