135 OPERATION ACR LTT TRACK DEVIATION PROBABLY CAUSED BY LONG DUTY TIME.

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ON OUR SEVENTH LEG OF THIS FLT. WE HAD FLOWN 6.5 HRS WITH LESS THAN 1 CUMULATIVE HOUR OF BREAKS. BELOW 14000' IT WAS HARD IFR. WE WERE ON OUR FILED ROUTE TO INTERCEPT AN ARWY; WE PASSED THROUGH THE ARWY BY 3 DEGS (AT OUR DISTANCE FROM THE VOR APPROX 3 MI). WE NOTED THE ARWY PASSING THROUGH AND TURNED TO INTERCEPT. AT NO TIME WAS THERE A FULL SCALE DEFLECTION. ATC THEN QUERIED US IF WE WERE ON OUR ASSIGNED ROUTING. LET IT BE NOTED THAT MY COPLT AND I WERE TO FLY 3 MORE HRS INTO THE NIGHT; OUR TOTAL DUTY TIME FOR THE DAY WAS 14.7 HRS AND WE CUMULATIVELY SHOT 18 APCHS 15 TO MINIMUMS WITH ONE MISSED APCH; ALL IN THE NE CORRIDOR. OUR FINAL APCH WAS AT BGM; NO APCH CTL; DRIVING RAIN; FOG AND 3/4 MI VIS AT 0020 IN THE MORNING. WE LOGGED 7 HRS OF ACTUAL IFR! CONTRIBUTING FACTOR: PLT FATIGUE; DUE TO BAD WX TIGHT SCHEDULING AND DISREGARD FOR CREW BREAKS BY MY COMPANY. WE FINALLY REFUSED TO FLY AT 2100 UNTIL PROVIDED A BREAK OUT OF THE ACFT WITH A MEAL. QUESTION: WHY DO PLTS WHO FLY THE LONGEST HRS; IN THE POOR WX OF THE LOW ALT STRUCTURE; AND LEAST COMPLEX ACFT; UNPROTECTED BY SANE FLT TIME AND DUTY REGS?