Narrative:

We were on the bonham 5 arrival into dfw. The aircraft was on autoplt and the FMC was navigating. When we contacted approach control we were told that we would be assigned a runway intersection. I loaded the ILS runway 36L into the FMC since this is the one we requested because we park on that side of the field. Additionally; this is necessary so that the FMC will navigation to dirkk intersection after stonz. I checked that all of the fixes were loaded properly and waited for a runway assignment. Finally as we were approaching stonz; approach control assigned us the ILS runway 35C. I quickly loaded this into the FMC and started looking for the approach chart for runway 35C. This took a few seconds since dfw has about 20 different approachs. As I was setting up the radios for the approach; we got an 'entering open segment' message from the FMC. I looked at the legs page of the FMC and our entire route had disappeared. Before I could re-enter the route; ATC issued us a heading to fly which I assume meant that we had overflown stonz. This indicated that instead of turning at stonz to proceed to dirkk; we would have continued southwest. From now on I'll have all of the approach plates out (in this case; there were 4 runways in use -- runway 36L; 35C; 35R; and 31). Also; it would be helpful if ATC would give us a runway assignment earlier. Also; I don't know why the FMC dropped our route out when I entered the new approach. When I get home I'll call our training department.

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Original NASA ASRS Text

Title: B737-300 COURSE DEV ON APCH TO DFW DUE TO FMC ENTRY OF A LAST MIN RWY CHANGE.

Narrative: WE WERE ON THE BONHAM 5 ARR INTO DFW. THE ACFT WAS ON AUTOPLT AND THE FMC WAS NAVING. WHEN WE CONTACTED APCH CTL WE WERE TOLD THAT WE WOULD BE ASSIGNED A RWY INTXN. I LOADED THE ILS RWY 36L INTO THE FMC SINCE THIS IS THE ONE WE REQUESTED BECAUSE WE PARK ON THAT SIDE OF THE FIELD. ADDITIONALLY; THIS IS NECESSARY SO THAT THE FMC WILL NAV TO DIRKK INTXN AFTER STONZ. I CHKED THAT ALL OF THE FIXES WERE LOADED PROPERLY AND WAITED FOR A RWY ASSIGNMENT. FINALLY AS WE WERE APCHING STONZ; APCH CTL ASSIGNED US THE ILS RWY 35C. I QUICKLY LOADED THIS INTO THE FMC AND STARTED LOOKING FOR THE APCH CHART FOR RWY 35C. THIS TOOK A FEW SECONDS SINCE DFW HAS ABOUT 20 DIFFERENT APCHS. AS I WAS SETTING UP THE RADIOS FOR THE APCH; WE GOT AN 'ENTERING OPEN SEGMENT' MESSAGE FROM THE FMC. I LOOKED AT THE LEGS PAGE OF THE FMC AND OUR ENTIRE RTE HAD DISAPPEARED. BEFORE I COULD RE-ENTER THE RTE; ATC ISSUED US A HDG TO FLY WHICH I ASSUME MEANT THAT WE HAD OVERFLOWN STONZ. THIS INDICATED THAT INSTEAD OF TURNING AT STONZ TO PROCEED TO DIRKK; WE WOULD HAVE CONTINUED SW. FROM NOW ON I'LL HAVE ALL OF THE APCH PLATES OUT (IN THIS CASE; THERE WERE 4 RWYS IN USE -- RWY 36L; 35C; 35R; AND 31). ALSO; IT WOULD BE HELPFUL IF ATC WOULD GIVE US A RWY ASSIGNMENT EARLIER. ALSO; I DON'T KNOW WHY THE FMC DROPPED OUR RTE OUT WHEN I ENTERED THE NEW APCH. WHEN I GET HOME I'LL CALL OUR TRAINING DEPT.

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.