ACR CARGO FLT HAS OMEGA NAV PROB; DRIFTS OFF COURSE.

Narrative

FLT LICZ TO KBGR: HAD NO PROBS WITH OMEGA OP UNTIL 53N 50W. AFTER 53N 50W NOTED DISCREPANCY IN OMEGAS. NOTIFIED GANDER RADIO OF THE PROB. WHEN IN VOR RECEPTION NOTED #2 OMEGA (NAV SYS IN USE) HAD DRIFTED. RESUMED NAV ON #1 OMEGA SYS AND VOR NAV. WHEN IN RADAR CONTACT; ASKED CTLR AND HE SAID WE HAD DRIFTED ABOUT 6 MI OFF COURSE. DON'T KNOW HOW FAR OFF COURSE WE WERE PRIOR TO THAT. WROTE UP #2 OMEGA IN LOGBOOK WHEN WE LANDED IN KBGR. DON'T KNOW WHAT CAUSED THE PROB. SUPPLEMENTAL INFO FROM ACN 237305: DISCONNECTED #2 FROM THE AUTOPLT AND CONTINUED FPR TO YAY (N5130 W5655.0). THIS IS A REPEAT OF OMEGA NAV VARIATION IN THE GANDER AREA. CAUSE UNKNOWN (TOTAL VARIATION ESTIMATED 18 NM). ADDITIONAL FACTOR/ POSSIBLE CONTRIBUTING FACTOR OF SLOWER THAN NORMAL CREW DISCREPANCY RECOGNITION: CREW FATIGUE. CREW HAD BEEN ON DUTY (WITHOUT ANY REST WHATSOEVER) FOR 17 HR 30 MINS OF A DUTY DAY OF 24 HRS 10 MINS. THIS INCLUDED TOTAL FLT TIME OF 15 HRS 5 MINS. THE PART 91 INTL FARS ARE LUDICROUS AND DEMAND (IN THE INTEREST OF SAFETY) A REVISION.