A B737 departing south on the seattle four SID dropped the SID routing when LNAV was selected and at...

Attributes
ACN	850422
Time
Date	200909
Local Time Of Day	0001-0600
Place
Locale Reference	SEA.Airport
State Reference	WA
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Initial Climb
Route In Use	SID SEATTLE 4
Flight Plan	IFR
Component
Aircraft Component	FMS/FMC
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Track / Heading All Types

Narrative:

This is the second report regarding FMC issues we are having on the seattle four departure. This time I watched the FMC carefully to see what was happening. On departure the seattle four departure is loaded in the box. LNAV gets selected and then the departure drops out and the FMC shows arrie as the active waypoint and the aircraft FD commands a turn of over 90 degrees of heading change to aarie. Heading select was selected then VOR/localizer to capture the 161 radial out of sea. Crew has to be on their toes to see that the turn is improper. Some sort of FMC software issue with the seattle four departure. I have seen this on two separate days with two different aircraft.

Original NASA ASRS Text

Title: A B737 departing south on the SEATTLE FOUR SID dropped the SID routing when LNAV was selected and attempted to turn right to ARRIE; the next active waypoint.

Narrative: This is the second report regarding FMC issues we are having on the SEATTLE FOUR DEPARTURE. This time I watched the FMC carefully to see what was happening. On departure the SEATTLE FOUR DEPARTURE is loaded in the box. LNAV gets selected and then the departure drops out and the FMC shows ARRIE as the active waypoint and the aircraft FD commands a turn of over 90 degrees of heading change to AARIE. Heading select was selected then VOR/LOC to capture the 161 radial out of SEA. Crew has to be on their toes to see that the turn is improper. Some sort of FMC software issue with the SEATTLE FOUR DEPARTURE. I have seen this on two separate days with two different aircraft.

Data retrieved from NASA's ASRS site as of April 2012 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.

A B737 departing south on the seattle four SID dropped the SID routing when LNAV was selected and attempted to turn right to arrie; the next active waypoint.