Narrative:

I am a lca giving a IOE on this widebody transport. After initial cockpit set-up, I had the IOE first officer do the captain portion of CDU programming, so he would be familiar with these duties and to determine if he knew these procedures. He performed this programming according to SOP. Setting the IRS position was accomplished using sin gate position. We subsequently got an 'enter IRS position' message on CDU. Gte position was reentered once and was accepted. I then verified the position with the coords at the singapore gate west they were same. Route was entered using co stored route, and was then checked by both myself and first officer in the plan mode. The complete route checked ok. Remainder of pushback start and taxi was normal. During this time we did not get an 'insufficient fuel' message. (This is important). In the briefing I had told first officer we would make raw data departure using VOR radials to illustrate that if pilot were to lose the map or magenta line he could still fly the departure. In this regard we were cleared for a rolling takeoff (first officer flying) and then switched to navigation display (nd) to VOR mode and tracked the VOR radial. We were eventually cleared direct to mevas waypoint. I made mevas the active waypoint on legs page but got no dashed line and noticed that magenta line was from left side of nd (in map mode) to mevas and not from airplane symbol to mevas. I asked for and received a vector for mevas. Then I began checking to see what was wrong. I checked legs page and route page first. I then checked our position on position init page and found the problem. Position (all IRS's and FMC) were in 'west' longitude and should have been east. Called company address and discussed problem. Decided to return to sin. We were vectored to final approach course. I manually tuned the ILS frequency to preclude any other error. After parking at sin gate I turned IRS's off, then to navigation and once again inserted the gate latitude/long from the sign at the gate. Position was accepted, (and this is also important) and we did not get any 'enter IRS position' message. I put in route again and checked ok remainder of trip was normal. In conclusion. No one can be 100 percent positive, but I am 95 percent positive that the gae position was correct. I believe this problem was due to either a software problem or some kind of map shift. The reason is that we only had to reenter IRS position once. We did not get any insufficient fuel message and back at the sin gate (return gate) we only had to insert the gate position one time.

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Original NASA ASRS Text

Title: A WDB CREW, ON A LINE CHK, HAD A GROSS NAVIGATIONAL ERROR. THE IRS SHOWED W LONGITUDE VICE THE PROPER E.

Narrative: I AM A LCA GIVING A IOE ON THIS WDB. AFTER INITIAL COCKPIT SET-UP, I HAD THE IOE FO DO THE CAPT PORTION OF CDU PROGRAMMING, SO HE WOULD BE FAMILIAR WITH THESE DUTIES AND TO DETERMINE IF HE KNEW THESE PROCS. HE PERFORMED THIS PROGRAMMING ACCORDING TO SOP. SETTING THE IRS POS WAS ACCOMPLISHED USING SIN GATE POS. WE SUBSEQUENTLY GOT AN 'ENTER IRS POS' MESSAGE ON CDU. GTE POS WAS REENTERED ONCE AND WAS ACCEPTED. I THEN VERIFIED THE POS WITH THE COORDS AT THE SINGAPORE GATE W THEY WERE SAME. RTE WAS ENTERED USING CO STORED RTE, AND WAS THEN CHKED BY BOTH MYSELF AND FO IN THE PLAN MODE. THE COMPLETE RTE CHKED OK. REMAINDER OF PUSHBACK START AND TAXI WAS NORMAL. DURING THIS TIME WE DID NOT GET AN 'INSUFFICIENT FUEL' MESSAGE. (THIS IS IMPORTANT). IN THE BRIEFING I HAD TOLD FO WE WOULD MAKE RAW DATA DEP USING VOR RADIALS TO ILLUSTRATE THAT IF PLT WERE TO LOSE THE MAP OR MAGENTA LINE HE COULD STILL FLY THE DEP. IN THIS REGARD WE WERE CLRED FOR A ROLLING TKOF (FO FLYING) AND THEN SWITCHED TO NAV DISPLAY (ND) TO VOR MODE AND TRACKED THE VOR RADIAL. WE WERE EVENTUALLY CLRED DIRECT TO MEVAS WAYPOINT. I MADE MEVAS THE ACTIVE WAYPOINT ON LEGS PAGE BUT GOT NO DASHED LINE AND NOTICED THAT MAGENTA LINE WAS FROM L SIDE OF ND (IN MAP MODE) TO MEVAS AND NOT FROM AIRPLANE SYMBOL TO MEVAS. I ASKED FOR AND RECEIVED A VECTOR FOR MEVAS. THEN I BEGAN CHKING TO SEE WHAT WAS WRONG. I CHKED LEGS PAGE AND RTE PAGE FIRST. I THEN CHKED OUR POS ON POS INIT PAGE AND FOUND THE PROBLEM. POS (ALL IRS'S AND FMC) WERE IN 'W' LONGITUDE AND SHOULD HAVE BEEN E. CALLED COMPANY ADDRESS AND DISCUSSED PROBLEM. DECIDED TO RETURN TO SIN. WE WERE VECTORED TO FINAL APCH COURSE. I MANUALLY TUNED THE ILS FREQ TO PRECLUDE ANY OTHER ERROR. AFTER PARKING AT SIN GATE I TURNED IRS'S OFF, THEN TO NAV AND ONCE AGAIN INSERTED THE GATE LAT/LONG FROM THE SIGN AT THE GATE. POS WAS ACCEPTED, (AND THIS IS ALSO IMPORTANT) AND WE DID NOT GET ANY 'ENTER IRS POS' MESSAGE. I PUT IN RTE AGAIN AND CHKED OK REMAINDER OF TRIP WAS NORMAL. IN CONCLUSION. NO ONE CAN BE 100 PERCENT POSITIVE, BUT I AM 95 PERCENT POSITIVE THAT THE GAE POS WAS CORRECT. I BELIEVE THIS PROBLEM WAS DUE TO EITHER A SOFTWARE PROBLEM OR SOME KIND OF MAP SHIFT. THE REASON IS THAT WE ONLY HAD TO REENTER IRS POS ONCE. WE DID NOT GET ANY INSUFFICIENT FUEL MESSAGE AND BACK AT THE SIN GATE (RETURN GATE) WE ONLY HAD TO INSERT THE GATE POS ONE TIME.

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.