Narrative:

After passing 400 ft AGL; my first officer called for LNAV. When I selected it the FD indicated a left turn and I immediately selected heading and legs page on the CDU. The legs page showed the first waypoint as gup; so I asked for vectors rather than try to 'fix' the box. When asked for the reason I said we erred and that was it; other than he said he had to make a report for all RNAV errors. How this happened is a mystery to me. I was conducting IOE and this was our second leg together and his first as the PF. We had a maintenance issue in las that resulted in a mechanic in my seat until shortly before scheduled departure time. When I got in my seat I did my flow and called for the before start check. After the check was complete; my first officer completed the clearance briefing and included the cowby RNAV departure. I then completed the departure briefing and including a review of the route pages and our RNAV procedures. I don't remember looking at the legs page. We pushed on time and on initial contact with ground we were told we were #1 for takeoff. As we approached the runway for departure; I called for the before takeoff check and watched my first officer complete his flow including the runway update button that showed runway 25R. The only possible explanation that I can think of is maybe the flight plan was altered but not executed; and when the loadsheet information was executed; it executed the alteration as well. I personally will check not only the route pages before departure; but the legs page as well. I will pay particular attention to the execute light as well. I was at fault for not having the legs page up prior to departure. I am sure I would have noticed the error if I had done so.

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Original NASA ASRS Text

Title: CHK PLT AND NEW FO ON B737-700 EXPERIENCE MOMENTARY TRACK DEV ON COWBY RNAV SID FROM LAS. FAULT INCORRECT FMS PROGRAMMING.

Narrative: AFTER PASSING 400 FT AGL; MY FO CALLED FOR LNAV. WHEN I SELECTED IT THE FD INDICATED A LEFT TURN AND I IMMEDIATELY SELECTED HDG AND LEGS PAGE ON THE CDU. THE LEGS PAGE SHOWED THE FIRST WAYPOINT AS GUP; SO I ASKED FOR VECTORS RATHER THAN TRY TO 'FIX' THE BOX. WHEN ASKED FOR THE REASON I SAID WE ERRED AND THAT WAS IT; OTHER THAN HE SAID HE HAD TO MAKE A RPT FOR ALL RNAV ERRORS. HOW THIS HAPPENED IS A MYSTERY TO ME. I WAS CONDUCTING IOE AND THIS WAS OUR SECOND LEG TOGETHER AND HIS FIRST AS THE PF. WE HAD A MAINT ISSUE IN LAS THAT RESULTED IN A MECHANIC IN MY SEAT UNTIL SHORTLY BEFORE SCHEDULED DEP TIME. WHEN I GOT IN MY SEAT I DID MY FLOW AND CALLED FOR THE BEFORE START CHK. AFTER THE CHK WAS COMPLETE; MY FO COMPLETED THE CLRNC BRIEFING AND INCLUDED THE COWBY RNAV DEP. I THEN COMPLETED THE DEP BRIEFING AND INCLUDING A REVIEW OF THE RTE PAGES AND OUR RNAV PROCS. I DON'T REMEMBER LOOKING AT THE LEGS PAGE. WE PUSHED ON TIME AND ON INITIAL CONTACT WITH GND WE WERE TOLD WE WERE #1 FOR TKOF. AS WE APCHED THE RWY FOR DEP; I CALLED FOR THE BEFORE TKOF CHK AND WATCHED MY FO COMPLETE HIS FLOW INCLUDING THE RWY UPDATE BUTTON THAT SHOWED RWY 25R. THE ONLY POSSIBLE EXPLANATION THAT I CAN THINK OF IS MAYBE THE FLT PLAN WAS ALTERED BUT NOT EXECUTED; AND WHEN THE LOADSHEET INFO WAS EXECUTED; IT EXECUTED THE ALTERATION AS WELL. I PERSONALLY WILL CHK NOT ONLY THE RTE PAGES BEFORE DEP; BUT THE LEGS PAGE AS WELL. I WILL PAY PARTICULAR ATTENTION TO THE EXECUTE LIGHT AS WELL. I WAS AT FAULT FOR NOT HAVING THE LEGS PAGE UP PRIOR TO DEP. I AM SURE I WOULD HAVE NOTICED THE ERROR IF I HAD DONE SO.

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.