Narrative:

As we approached duwop intersection on the mahem RNAV one arrival, we were given a runway change from runway 26 to runway 25L. When we reprogrammed the FMC for runway 25L there was a route discontinuity after duwop. As we line selected intersection bline to bring under duwop we crossed over duwop and the LNAV disengaged because we did not have time to execute the new routing. I immediately requested vectors for runway 25L. Approach asked what had happened, I explained it to him and he gave us a phone number to call for a possible deviation. After landing, I called phx approach and talked with a supervisor. After explaining the situation to him, he said that there would be no deviation filed, but he did caution me that the exact deviation had occurred the previous day. He said that there were numerous deviations everyday and that something needed to change to reduce the number of deviations. I think that we took the expected action by asking for vectors immediately. The supervisor seemed to convey that anytime the LNAV disengaged, even if we requested immediate vectors, that there could be a deviation filed. I am not sure what could have been done to prevent this deviation other than waiting to reprogram the FMC after making the turn at duwop. However, in other scenarios, to different airports/runways, it might be necessary to immediately reprogram the FMC for the correct waypoints on an RNAV arrival. ATC should not issue runway changes just prior to a fix that could create reprogramming requirements that will create a route discontinuity every time until you have time to re-execute the new correct routing. I'm not sure there is a correct answer excerpt to be aware that this will occur while changing runways on an RNAV arrival every time.

Google
 

Original NASA ASRS Text

Title: B737 FLC TRY TO REPROGRAM RWY CHANGE AT PHX WHILE FLYING THE MAHEM RNAV STAR AND ENCOUNTER FMS PROBS, ADVISING P50 AS THEY MISS A PUBLISHED TURN THAT THEY NEED RADAR VECTORS TO FINAL.

Narrative: AS WE APCHED DUWOP INTXN ON THE MAHEM RNAV ONE ARR, WE WERE GIVEN A RWY CHANGE FROM RWY 26 TO RWY 25L. WHEN WE REPROGRAMMED THE FMC FOR RWY 25L THERE WAS A RTE DISCONTINUITY AFTER DUWOP. AS WE LINE SELECTED INTXN BLINE TO BRING UNDER DUWOP WE CROSSED OVER DUWOP AND THE LNAV DISENGAGED BECAUSE WE DID NOT HAVE TIME TO EXECUTE THE NEW ROUTING. I IMMEDIATELY REQUESTED VECTORS FOR RWY 25L. APCH ASKED WHAT HAD HAPPENED, I EXPLAINED IT TO HIM AND HE GAVE US A PHONE NUMBER TO CALL FOR A POSSIBLE DEV. AFTER LNDG, I CALLED PHX APCH AND TALKED WITH A SUPVR. AFTER EXPLAINING THE SIT TO HIM, HE SAID THAT THERE WOULD BE NO DEV FILED, BUT HE DID CAUTION ME THAT THE EXACT DEV HAD OCCURRED THE PREVIOUS DAY. HE SAID THAT THERE WERE NUMEROUS DEVS EVERYDAY AND THAT SOMETHING NEEDED TO CHANGE TO REDUCE THE NUMBER OF DEVS. I THINK THAT WE TOOK THE EXPECTED ACTION BY ASKING FOR VECTORS IMMEDIATELY. THE SUPVR SEEMED TO CONVEY THAT ANYTIME THE LNAV DISENGAGED, EVEN IF WE REQUESTED IMMEDIATE VECTORS, THAT THERE COULD BE A DEV FILED. I AM NOT SURE WHAT COULD HAVE BEEN DONE TO PREVENT THIS DEV OTHER THAN WAITING TO REPROGRAM THE FMC AFTER MAKING THE TURN AT DUWOP. HOWEVER, IN OTHER SCENARIOS, TO DIFFERENT ARPTS/RWYS, IT MIGHT BE NECESSARY TO IMMEDIATELY REPROGRAM THE FMC FOR THE CORRECT WAYPOINTS ON AN RNAV ARR. ATC SHOULD NOT ISSUE RWY CHANGES JUST PRIOR TO A FIX THAT COULD CREATE REPROGRAMMING REQUIREMENTS THAT WILL CREATE A RTE DISCONTINUITY EVERY TIME UNTIL YOU HAVE TIME TO RE-EXECUTE THE NEW CORRECT ROUTING. I'M NOT SURE THERE IS A CORRECT ANSWER EXCERPT TO BE AWARE THAT THIS WILL OCCUR WHILE CHANGING RWYS ON AN RNAV ARR EVERY 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.