Narrative:

Flight licz to kbgr: had no problems with omega operation until 53N 50W. After 53N 50W noted discrepancy in omegas. Notified gander radio of the problem. When in VOR reception noted #2 omega (navigation system in use) had drifted. Resumed navigation on #1 omega system and VOR navigation. When in radar contact, asked controller 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 problem. Supplemental information from acn 237305: disconnected #2 from the autoplt and continued fpr to yay (N5130 W5655.0). This is a repeat of omega navigation 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 hour 30 mins of a duty day of 24 hours 10 mins. This included total flight time of 15 hours 5 mins. The part 91 international FARS are ludicrous and demand (in the interest of safety) a revision.

Google
 

Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.