Narrative:

After takeoff from lax westbound, we were cleared left turn direct lax VOR, as filed. Passing lax, the FMC called for a right turn to sli VOR. First officer hand-flying. I noticed on map display after sli route was almost 90 degree left turn to dag. Requested direct dag and received direct. Moments later ATC asked if we knew where we were, and that we were 15 mi south of loop 8 departure route. We were told to turn left to 330 degree heading and then cleared direct dag. Somehow the FMC had dumped out the loop 8 departure and had us going to sli and then dag. While we were doing this clearance and trying to figure out what may have gone wrong, we passed 18000' and didn't set altimeters to 29.92. After level off at 37000', ATC asked our altitude and I replied 37000'. We were told mode C had us 300' low. Altimeter was 30.23'. Set altimeter and remainder of flight was normal. One of the problems was that I was relying on the FMC too much for departure and not x-chking with departure plate. New, first glass cockpit. Supplemental information from acn 174704: captain and I reviewed the SID several times and the made changes in the procedure when we were given a runway change. We were expecting lax 24L and we took off on 25R. I made the changes in the FMC and everything proceeded normally. We briefed the changes and installed a fix in the FMC to aid in the departure. Later found out there is a software glitch in the loop 8 SID that has not been corrected. This occurs when there is a runway change, which is what happened to us. One can get lost or misdirected, even with all the latest navigation tech. In the future I will rely more on traditional navaids for FMC backup. I also made the mistake of using too small a scale for the navigation display. On a larger scale I would have seen the error and would not have flown to the south.

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Original NASA ASRS Text

Title: ADVTECH ACR WDB EXPERIENCES MINOR FMS PROBLEM, BUT FAILS TO CATCH ERROR AND SUFFERS TRACK DEVIATION AND ALT UNDERSHOOT DUE MISSET ALTIMETER.

Narrative: AFTER TKOF FROM LAX WBND, WE WERE CLRED LEFT TURN DIRECT LAX VOR, AS FILED. PASSING LAX, THE FMC CALLED FOR A RIGHT TURN TO SLI VOR. F/O HAND-FLYING. I NOTICED ON MAP DISPLAY AFTER SLI RTE WAS ALMOST 90 DEG LEFT TURN TO DAG. REQUESTED DIRECT DAG AND RECEIVED DIRECT. MOMENTS LATER ATC ASKED IF WE KNEW WHERE WE WERE, AND THAT WE WERE 15 MI S OF LOOP 8 DEP RTE. WE WERE TOLD TO TURN LEFT TO 330 DEG HDG AND THEN CLRED DIRECT DAG. SOMEHOW THE FMC HAD DUMPED OUT THE LOOP 8 DEP AND HAD US GOING TO SLI AND THEN DAG. WHILE WE WERE DOING THIS CLRNC AND TRYING TO FIGURE OUT WHAT MAY HAVE GONE WRONG, WE PASSED 18000' AND DIDN'T SET ALTIMETERS TO 29.92. AFTER LEVEL OFF AT 37000', ATC ASKED OUR ALT AND I REPLIED 37000'. WE WERE TOLD MODE C HAD US 300' LOW. ALTIMETER WAS 30.23'. SET ALTIMETER AND REMAINDER OF FLT WAS NORMAL. ONE OF THE PROBS WAS THAT I WAS RELYING ON THE FMC TOO MUCH FOR DEP AND NOT X-CHKING WITH DEP PLATE. NEW, FIRST GLASS COCKPIT. SUPPLEMENTAL INFO FROM ACN 174704: CAPT AND I REVIEWED THE SID SEVERAL TIMES AND THE MADE CHANGES IN THE PROC WHEN WE WERE GIVEN A RWY CHANGE. WE WERE EXPECTING LAX 24L AND WE TOOK OFF ON 25R. I MADE THE CHANGES IN THE FMC AND EVERYTHING PROCEEDED NORMALLY. WE BRIEFED THE CHANGES AND INSTALLED A FIX IN THE FMC TO AID IN THE DEP. LATER FOUND OUT THERE IS A SOFTWARE GLITCH IN THE LOOP 8 SID THAT HAS NOT BEEN CORRECTED. THIS OCCURS WHEN THERE IS A RWY CHANGE, WHICH IS WHAT HAPPENED TO US. ONE CAN GET LOST OR MISDIRECTED, EVEN WITH ALL THE LATEST NAV TECH. IN THE FUTURE I WILL RELY MORE ON TRADITIONAL NAVAIDS FOR FMC BACKUP. I ALSO MADE THE MISTAKE OF USING TOO SMALL A SCALE FOR THE NAV DISPLAY. ON A LARGER SCALE I WOULD HAVE SEEN THE ERROR AND WOULD NOT HAVE FLOWN TO THE S.

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.