B737-900 captain describes the FMC's reaction to a runway change entered during an RNAV arrival. A r...

Narrative:

We were descending on the hawkz 4 arrival approaching pikez intersection when we received a runway change from ATC to 16C. The first officer selected 16c in the FMS; which caused a disconnect on the legs page and took the autopilot out of LNAV just as the aircraft was just about to make the turn from pikez to cofay . I heading selected the aircraft to the right toward cofay while the first officer fixed the disconnect in about 2 seconds. LNAV was reengaged. The aircraft was never off course and the ATC controller did not say anything. The point of this report is that this is a common occurrence with the FMC when a runway change is made during the middle of the arrival. The fixes seem to double up; in this case pikez was at the top of the legs page followed by a disconnect and then below that pikez intersection was there again below the disconnect. I don't know if it is a software problem or what but it occurs often with a runway change.

Original NASA ASRS Text

Title: B737-900 Captain describes the FMC's reaction to a runway change entered during an RNAV arrival. A route discontinuity is created and the autopilot reverts to heading hold.

Narrative: We were descending on the HAWKZ 4 arrival approaching PIKEZ intersection when we received a runway change from ATC to 16C. The first officer selected 16c in the FMS; which caused a disconnect on the legs page and took the autopilot out of LNAV just as the aircraft was just about to make the turn from PIKEZ to COFAY . I heading selected the aircraft to the right toward COFAY while the first officer fixed the disconnect in about 2 seconds. LNAV was reengaged. The aircraft was never off course and the ATC controller did not say anything. The point of this report is that this is a common occurrence with the FMC when a runway change is made during the middle of the arrival. The fixes seem to double up; in this case PIKEZ was at the top of the legs page followed by a disconnect and then below that PIKEZ intersection was there again below the disconnect. I don't know if it is a software problem or what but it occurs often with a runway change.

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.

Attributes
ACN	1221964
Time
Date	201412
Local Time Of Day	0001-0600
Place
Locale Reference	SEA.Airport
State Reference	WA
Aircraft 1
Make Model Name	B737-900
Operating Under FAR Part	Part 121
Flight Phase	Descent
Component
Aircraft Component	FMS/FMC
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe

B737-900 captain describes the FMC's reaction to a runway change entered during an RNAV arrival. A route discontinuity is created and the autopilot reverts to heading hold.