Narrative:

Both pilots verified route and gate position. Prior to takeoff runway alignment was verified. Departure control cleared us direct to intersection. FMC showed us on course; however; departure control informed us we were 60 degrees off and gave us a heading to intercept the airway south of VOR. Again FMC showed us on course. In light of our previous experience; we elected to verify the FMC's with VOR's and discovered the FMC's were at least 15 miles off. FMC's would not update off VOR's. I elected to return to ZZZ. I don't know what caused the failure; however; maintenance was still working on it 9 hours later. Had failure occurred in mountainous terrain in IMC; the results could have been disastrous. As a result; I phoned the base chief pilots office and requested the post repair crew be given a 'heads up;' as to our experience in order they watch FMC performance carefully.supplemental information from acn 761191: on climb-out; departure cleared us to intersection. As the non-flying pilot I selected direct intersection; verified it with the captain and executed it. At the captain's call I engaged l-nav. Departure asked us to verify direct intersection which I did and then proceeded to verify it off of the VOR. It looked close but I couldn't say initially that it was perfectly accurate. We were then given a heading to hold and I told the controller that I questioned our navigation system accuracy. We switched to another center and were cleared direct to VOR. I dialed in the VOR frequency and we proceeded utilizing VOR navigation. We then received a FMS message-purge update position 2; followed by IRS navigation only. The captain ACARS dispatch and then decided to return to ZZZ. We made an overweight landing; reasoning that it was more prudent than circling to burn down to landing weight.callback conversation with reporter acn 762140 revealed the following information: the reporter emphasized that the crew performed the preflight alignment properly and did not get the flashing align lights indicating a position error. On takeoff a runway alignment was completed with no error indicated. However very shortly after takeoff a navigation error developed. While troubleshooting; the reporter stated that no VOR stations were identified on the progress page to indicate their usage for continuous FMS position update. There was never an error message indicating a problem much less what type of problem. Upon return to the departure airport; maintenance took the aircraft and when the reporter checked with them 12 hours later; no cause had been identified. The reporter is concerned about this aircraft being flown where terrain is an issue. Overall the reporter feels this aircraft's problems may fit into the aging aircraft category.

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Original NASA ASRS Text

Title: A B767-200 FMS DID NOT PERFORM VOR UPDATES AFTER TKOF AND DEVIATED 15 NM FROM TRACK BEFORE RETURNING TO LAND.

Narrative: BOTH PLTS VERIFIED RTE AND GATE POSITION. PRIOR TO TAKEOFF RWY ALIGNMENT WAS VERIFIED. DEP CTL CLRED US DIRECT TO INTXN. FMC SHOWED US ON COURSE; HOWEVER; DEP CTL INFORMED US WE WERE 60 DEGS OFF AND GAVE US A HEADING TO INTERCEPT THE AIRWAY S OF VOR. AGAIN FMC SHOWED US ON COURSE. IN LIGHT OF OUR PREVIOUS EXPERIENCE; WE ELECTED TO VERIFY THE FMC'S WITH VOR'S AND DISCOVERED THE FMC'S WERE AT LEAST 15 MILES OFF. FMC'S WOULD NOT UPDATE OFF VOR'S. I ELECTED TO RETURN TO ZZZ. I DON'T KNOW WHAT CAUSED THE FAILURE; HOWEVER; MAINT WAS STILL WORKING ON IT 9 HRS LATER. HAD FAILURE OCCURRED IN MOUNTAINOUS TERRAIN IN IMC; THE RESULTS COULD HAVE BEEN DISASTROUS. AS A RESULT; I PHONED THE BASE CHIEF PLTS OFFICE AND REQUESTED THE POST REPAIR CREW BE GIVEN A 'HEADS UP;' AS TO OUR EXPERIENCE IN ORDER THEY WATCH FMC PERFORMANCE CAREFULLY.SUPPLEMENTAL INFO FROM ACN 761191: ON CLIMB-OUT; DEP CLRED US TO INTXN. AS THE NON-FLYING PLT I SELECTED DIRECT INTXN; VERIFIED IT WITH THE CAPT AND EXECUTED IT. AT THE CAPT'S CALL I ENGAGED L-NAV. DEP ASKED US TO VERIFY DIRECT INTXN WHICH I DID AND THEN PROCEEDED TO VERIFY IT OFF OF THE VOR. IT LOOKED CLOSE BUT I COULDN'T SAY INITIALLY THAT IT WAS PERFECTLY ACCURATE. WE WERE THEN GIVEN A HEADING TO HOLD AND I TOLD THE CTLR THAT I QUESTIONED OUR NAV SYSTEM ACCURACY. WE SWITCHED TO ANOTHER CTR AND WERE CLRED DIRECT TO VOR. I DIALED IN THE VOR FREQ AND WE PROCEEDED UTILIZING VOR NAV. WE THEN RECEIVED A FMS MESSAGE-PURGE UPDATE POS 2; FOLLOWED BY IRS NAV ONLY. THE CAPT ACARS DISPATCH AND THEN DECIDED TO RETURN TO ZZZ. WE MADE AN OVERWT LNDG; REASONING THAT IT WAS MORE PRUDENT THAN CIRCLING TO BURN DOWN TO LNDG WT.CALLBACK CONVERSATION WITH RPTR ACN 762140 REVEALED THE FOLLOWING INFO: THE RPTR EMPHASIZED THAT THE CREW PERFORMED THE PREFLT ALIGNMENT PROPERLY AND DID NOT GET THE FLASHING ALIGN LIGHTS INDICATING A POSITION ERROR. ON TKOF A RWY ALIGNMENT WAS COMPLETED WITH NO ERROR INDICATED. HOWEVER VERY SHORTLY AFTER TKOF A NAV ERROR DEVELOPED. WHILE TROUBLESHOOTING; THE RPTR STATED THAT NO VOR STATIONS WERE IDENTIFIED ON THE PROGRESS PAGE TO INDICATE THEIR USAGE FOR CONTINUOUS FMS POSITION UPDATE. THERE WAS NEVER AN ERROR MSG INDICATING A PROBLEM MUCH LESS WHAT TYPE OF PROBLEM. UPON RETURN TO THE DEP ARPT; MAINT TOOK THE ACFT AND WHEN THE RPTR CHECKED WITH THEM 12 HOURS LATER; NO CAUSE HAD BEEN IDENTIFIED. THE RPTR IS CONCERNED ABOUT THIS ACFT BEING FLOWN WHERE TERRAIN IS AN ISSUE. OVERALL THE RPTR FEELS THIS ACFT'S PROBLEMS MAY FIT INTO THE AGING ACFT CATEGORY.

Data retrieved from NASA's ASRS site as of January 2009 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.