HDG TRACK DEV IN FLC NON ADHERENCE TO ATC CLRNC.

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I WAS THE PNF; THE FO WAS FLYING. ACFT TYPE IS J-32 WITHOUT AUTOPLT. WE WERE TO FLY THE MRB 006 DEG RADIAL TO HGR VOR THEN THE 052 DEG RADIAL TO HAR VOR. WE WERE AT 11000 FT AND ON COURSE WHEN I STARTED TO FILL OUT THE LOGBOOK. I LOOKED UP TO CHK; WE WERE ON COURSE 006 DEGS/7-8 OUT; ALT 11000 FT. A FEW MINS LATER; I NOTICED WE WERE 24 MI OUT OF MFB AND STILL ON THE 006 DEG RADIAL. I ADVISED MY FO TO TURN R TO A NEW HDG TO INTERCEPT THE 052 DEG RADIAL OF HGR. A FEW SECONDS LATER; ZNY ADVISED US THAT WE WERE 8 MI N OF COURSE AND ASKED IF WE AGREED. I ADVISED CTR THAT WE SHOWED N OF COURSE AND THAT WE WERE CORRECTING. ATC ADVISED THAT WE FLY HDG 050 DEGS. WE COMPLIED. SHORTLY AFTER THAT; ATC SAID TO FLY HDG 030 DEGS FOR TFC; THEN CLRED US DIRECTLY TO SELLINGSGROVE VOR; WHICH IS ON COURSE. NO FURTHER COMMENTS WERE MADE BY ATC AND WE WERE HANDED OFF. FROM A HUMAN FACTORS POINT OF VIEW; CONSIDER THIS: PREVIOUS DAY -- 13.6 HRS OF DUTY; 8.2 FLT HRS. RPTED FOR WORK AT AM00. DUTY END AT XX00. DROVE HOME AND WENT TO BED AT XY00. RPTED BACK TO WORK AT XY00 PLUS 8 THE FOLLOWING DAY WITH ONLY 5 1/2 HRS OF SLEEP; AND WORKED 13 HRS WITH 8.1 HRS OF FLT. THERE WERE NO BREAKS FOR BREAKFAST; LUNCH; DINNER IN EITHER DAY. I FEEL FATIGUE AND CREW ABUSE AS A PRIMARY FACTOR.