Narrative:

En route from bos to dfw, we were cruising at FL350 and using omega as primary navigation. Passing overhead lancaster (lrp) we verified our position with the omega at XX53Z with 37900 pounds of fuel. Passing lrp 11 NM outbound we verified the outbound track on J6 toward martinsburg (mrb). By 45 NM southwest of lrp we were 7-10 NM south of course. ZNY (frequency 133.475) called us south of course and gave us a vector to intercept J6 into mrb. In a period of 3-4 mins, the omega had a 7-10 NM error. We corrected back on course using VOR/DME. Overhead mrb, verified by VOR/DME, we performed an ONS precision position update in accordance with the pom. The omega position was 10 NM north of our actual position (mrb coordinates are N3923.1 W7750.9. Omega coordinates showed N3933.3 W7752.3. After we updated the omega at mrb, we used it for navigation again, monitoring it very closely. It functioned normally after the update. We called flight control dispatcher and advised him of the omega anomaly between lrp and mrb and requested he issue a NOTAM to advise our omega users of the anomaly since the omega worked normally after mrb. Callback conversation with reporter revealed the following information: callback was accomplished to determine if pilot had experience and competency to operate the omega system. Reporter had a total of 7 yrs experience with the omega system. He had a distrust of the system which caused him to xchk and update frequently. He had never had as great a course deviation as in this instance. He never checked his VLF pages for weak propagation as he never got a warning light that propagation might be a problem. The aircraft only had 1 set on board so there was no chance to see or compare with another set if there was a divergence between 2 sets. Pilot verified omega was loaded properly with the first officer prior to departure. Position was checked over the VOR prior to the course deviation. After crossing the VOR the aircraft heading changed more than what was required, it was a gradual change of 2-3 degrees of bank, not noticeable by the flight crew. After flying 42 mi the aircraft was 10 mi of course. Center called and gave them a heading into the next waypoint. Omega was updated at the next waypoint and from thereafter, it was always on track. Reporter's chief pilot accused him of making a operational error with the quip. Reporter stated to him, that if he hadn't used the omega properly he would have filed the ASRS report and not have said anything about it to the company. He did both reports as he was upset about the omega performance. Reporter is convinced he did nothing wrong in operating the omega.

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Original NASA ASRS Text

Title: COURSE DEV USING OMEGA NAV.

Narrative: ENRTE FROM BOS TO DFW, WE WERE CRUISING AT FL350 AND USING OMEGA AS PRIMARY NAV. PASSING OVERHEAD LANCASTER (LRP) WE VERIFIED OUR POS WITH THE OMEGA AT XX53Z WITH 37900 LBS OF FUEL. PASSING LRP 11 NM OUTBOUND WE VERIFIED THE OUTBOUND TRACK ON J6 TOWARD MARTINSBURG (MRB). BY 45 NM SW OF LRP WE WERE 7-10 NM S OF COURSE. ZNY (FREQ 133.475) CALLED US S OF COURSE AND GAVE US A VECTOR TO INTERCEPT J6 INTO MRB. IN A PERIOD OF 3-4 MINS, THE OMEGA HAD A 7-10 NM ERROR. WE CORRECTED BACK ON COURSE USING VOR/DME. OVERHEAD MRB, VERIFIED BY VOR/DME, WE PERFORMED AN ONS PRECISION POS UPDATE IAW THE POM. THE OMEGA POS WAS 10 NM N OF OUR ACTUAL POS (MRB COORDINATES ARE N3923.1 W7750.9. OMEGA COORDINATES SHOWED N3933.3 W7752.3. AFTER WE UPDATED THE OMEGA AT MRB, WE USED IT FOR NAV AGAIN, MONITORING IT VERY CLOSELY. IT FUNCTIONED NORMALLY AFTER THE UPDATE. WE CALLED FLT CTL DISPATCHER AND ADVISED HIM OF THE OMEGA ANOMALY BTWN LRP AND MRB AND REQUESTED HE ISSUE A NOTAM TO ADVISE OUR OMEGA USERS OF THE ANOMALY SINCE THE OMEGA WORKED NORMALLY AFTER MRB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CALLBACK WAS ACCOMPLISHED TO DETERMINE IF PLT HAD EXPERIENCE AND COMPETENCY TO OPERATE THE OMEGA SYS. RPTR HAD A TOTAL OF 7 YRS EXPERIENCE WITH THE OMEGA SYS. HE HAD A DISTRUST OF THE SYS WHICH CAUSED HIM TO XCHK AND UPDATE FREQUENTLY. HE HAD NEVER HAD AS GREAT A COURSE DEV AS IN THIS INSTANCE. HE NEVER CHKED HIS VLF PAGES FOR WEAK PROPAGATION AS HE NEVER GOT A WARNING LIGHT THAT PROPAGATION MIGHT BE A PROB. THE ACFT ONLY HAD 1 SET ON BOARD SO THERE WAS NO CHANCE TO SEE OR COMPARE WITH ANOTHER SET IF THERE WAS A DIVERGENCE BTWN 2 SETS. PLT VERIFIED OMEGA WAS LOADED PROPERLY WITH THE FO PRIOR TO DEP. POS WAS CHKED OVER THE VOR PRIOR TO THE COURSE DEV. AFTER XING THE VOR THE ACFT HDG CHANGED MORE THAN WHAT WAS REQUIRED, IT WAS A GRADUAL CHANGE OF 2-3 DEGS OF BANK, NOT NOTICEABLE BY THE FLC. AFTER FLYING 42 MI THE ACFT WAS 10 MI OF COURSE. CTR CALLED AND GAVE THEM A HDG INTO THE NEXT WAYPOINT. OMEGA WAS UPDATED AT THE NEXT WAYPOINT AND FROM THEREAFTER, IT WAS ALWAYS ON TRACK. RPTR'S CHIEF PLT ACCUSED HIM OF MAKING A OPERATIONAL ERROR WITH THE QUIP. RPTR STATED TO HIM, THAT IF HE HADN'T USED THE OMEGA PROPERLY HE WOULD HAVE FILED THE ASRS RPT AND NOT HAVE SAID ANYTHING ABOUT IT TO THE COMPANY. HE DID BOTH RPTS AS HE WAS UPSET ABOUT THE OMEGA PERFORMANCE. RPTR IS CONVINCED HE DID NOTHING WRONG IN OPERATING THE OMEGA.

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.