Narrative:

Reprogramming selected approach caused route discontinuity that resulted in track deviation. On wleee 5 arrival to aus; just prior to xwing waypoint; we reprogrammed approach from RNAV (rnp) Z 17L to ILS 17L. (Lowering weather made ILS a better choice.) selected 17L jedye transition in CDU; examined legs page for route from jedye to runway; and confirmed with first officer. When executed; it caused route discontinuity (discontinuity on CDU scratch pad); and FMC mode changed to control wheel steering (cws). I attempted to follow magenta track; which still displayed desired route; on navigation display (nd) using heading select; but was unable to maintain track after xwing. Approach control assigned a heading. We continued with radar vectors to ILS 17L. The remainder of flight was uneventful. I did not expect that a change to the approach for the same runway as previously selected would result in a route discontinuity. When I examined the legs page prior to executing the change; I was focused on the new portion of the route; from jedye to ILS 17L to runway. I failed to note that the route in the legs page contained a discontinuity. Obviously; we changed runways and approaches very frequently during arrival. I'm unsure of which conditions (combination of arrival; approach; and runway) will cause a discontinuity and which will not. During the three remaining flights of this trip; each arrival involved a runway or approach change; reprogramming the FMC/CDU did not result in a discontinuity in any of these situations. I understand; now; that the most important thing is to ensure; prior to executing the change; that the first point on the legs page is the next point on the arrival; because that's where the aircraft will go. [I should] confirm that the legs page accurately reflects the remainder of the route to be flown prior to executing a route change. Training on FMC system to make pilots aware of which conditions; when changing runway or approach; will cause a route discontinuity and which will not. Modify FMC software so that modifications to runway or approach behave consistently.

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Original NASA ASRS Text

Title: B737-700 Captain reported a track deviation occurred on arrival into AUS when a late runway change required FMS reprogramming; during which a route discontinuity resulted.

Narrative: Reprogramming selected approach caused route discontinuity that resulted in track deviation. On WLEEE 5 Arrival to AUS; just prior to XWING waypoint; we reprogrammed approach from RNAV (RNP) Z 17L to ILS 17L. (Lowering weather made ILS a better choice.) Selected 17L JEDYE transition in CDU; examined LEGS page for route from JEDYE to runway; and confirmed with First Officer. When executed; it caused route discontinuity (discontinuity on CDU scratch pad); and FMC mode changed to Control Wheel Steering (CWS). I attempted to follow magenta track; which still displayed desired route; on navigation display (ND) using Heading Select; but was unable to maintain track after XWING. Approach Control assigned a heading. We continued with radar vectors to ILS 17L. The remainder of flight was uneventful. I did not expect that a change to the approach for the same runway as previously selected would result in a route discontinuity. When I examined the LEGS page prior to executing the change; I was focused on the new portion of the route; from JEDYE to ILS 17L to runway. I failed to note that the route in the LEGS page contained a discontinuity. Obviously; we changed runways and approaches very frequently during arrival. I'm unsure of which conditions (combination of arrival; approach; and runway) will cause a discontinuity and which will not. During the three remaining flights of this trip; each arrival involved a runway or approach change; reprogramming the FMC/CDU did not result in a discontinuity in any of these situations. I understand; now; that the most important thing is to ensure; prior to executing the change; that the first point on the LEGS page is the next point on the arrival; because that's where the aircraft will go. [I should] confirm that the LEGS page accurately reflects the remainder of the route to be flown prior to executing a route change. Training on FMC system to make pilots aware of which conditions; when changing runway or approach; will cause a route discontinuity and which will not. Modify FMC software so that modifications to runway or approach behave consistently.

Data retrieved from NASA's ASRS site 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.