B757 CREW DID NOT FLY THE ASSIGNED HDG FOR INTERCEPT OF SID RADIAL.

Narrative

AFTER DEPARTING CVG; WE WERE CLBING AND CLRED TO INTERCEPT THE BLUEGRASS 3 DEP; IIU (LOUISVILLE) TRANSITION; ON COURSE. CAPT WAS HAND FLYING AND I WAS PROGRAMMING FMS. WE WERE GIVEN THE CLRNC 'ACR XXX; TURN R; HDG 240 DEGS; JOIN THE BLUEGRASS 3.' I SELECTED 240 DEG HDG AND THE CAPT TURNED. THE CAPT HAD PUT THE BLUEGRASS3.IIU ON THE FMC PRIOR TO DEP AND WHEN GIVEN THE CLRNC TO JOIN; IIU WAS SHOWN ON LINE 1L OF THE FMC AS THE ACTIVE WAYPOINT. THE COMPUTER SHOWED THE COURSE TO BE 218 DEGS DIRECT TO IIU AND PRIOR TO ACCEPTING THAT; I LOOKED AT THE CHART AND SAW IT WAS A 221 DEG RADIAL OUT OF CVG TO IIU. I DIDN'T KNOW WHETHER THE CAPT HAD EVER HAD CVG IN THE FMS AT ALL OR WHERE THE 218 DEGS CAME FROM (SOMETIMES THE FMC CHANGES COURSE 1 DEG OR 2) SO REASONING WE WERE CLOSE TO THE CVG VOR; I PUT IN 221 DEGS AS THE 'INTERCEPT LEG TO' COURSE. I LOOKED AT THE MAP; CONFIRMED THAT THE COURSE OVERLAID WITH THE CVG VOR; EXECUTED AND SELECTED NAV (LNAV). THE COURSE WAS IMMEDIATELY CAPTURED. SHORTLY THEREAFTER; ATC SAID OUR HDG SHOULD BE 240 DEGS TO INTERCEPT THE COURSE. I SAID WE WERE ON COURSE. SHE SAID WE WERE 5 MI E OF COURSE. I WENT BACK TO THE CHART AS THE CAPT FLEW 240 DEGS AND PUT THE 216 DEG COURSE INTO IIU; WHICH THE CAPT DID NOT LIKE. HE SAID GO DIRECT CVG THEN REMOVE THE DISCONTINUITY BTWN CVG AND IIU; THEN DIRECT INTERCEPT THE LEG TO IIU (WHICH WILL WORK; BUT IS KEYSTROKE INTENSE); BUT I DID SO AND GOT A 219 DEG INBOUND COURSE TO IIU; WHICH WE INTERCEPTED AND NOTHING MORE WAS SAID. I DON'T THINK THAT THERE WAS ANY LOSS OF SEPARATION. COMMENTS: AHARS EQUIPPED ACFT -- NOT AS ACCURATE AS IRS. CAPT HAND FLEW THROUGHOUT THIS INSTEAD OF PUTTING AUTOPLT ON AND HELPING. I REALLY DON'T BELIEVE A 2 DEG ERROR IS SIGNIFICANT AT +/-35 MI FROM A VOR STATION. OLDER ACFT AND WITH NO RNAV CAN'T EVEN DO THAT WELL. I DID THE MATH AND COULDN'T GET A 5 MI ERROR OUT OF A 2-6 DEG ERROR (DEPENDING ON WHICH FMC COURSE YOU TRUST; THE ONE IT GENERATED; OR MY 216 DEG COURSE MANUALLY INSERTED; WHICH I TRUST MORE).