A B737-300 flying an RNAV departure with no moving map; no GPS and a single FMC had a track deviatio...

Attributes
ACN	952593
Time
Date	201106
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	Climb
Flight Plan	IFR
Component
Aircraft Component	FMS/FMC
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 264 Flight Crew Type 13000
Person 2
Function	Pilot Not Flying First Officer
Experience	Flight Crew Last 90 Days 251 Flight Crew Type 5200
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Track / Heading All Types

Narrative:

[We were] assigned an RNAV departure and a standard transition. Departure was loaded into FMC and verified by both pilots at the gate. Runway 25R was also verified as the correct departure runway. Runway update was complete at the end of 25R and both navigation switches with placed in the down position. LNAV was selected at 400 ft AGL. At 1;000 ft AGL; legs page was selected on the single FMC. Our first waypoint; verified on legs page1; was 'magenta' and at the top left position. Command bars began to show a left turn for the waypoint. The wind at the airport was southerly in direction. The FMC showed a 235 heading to the waypoint. I immediately assumed a strong south wind and engaged the autopilot shortly after 1;000 ft. Departure ATC immediately said we made our left turn to early. All flight operations manual procedures were followed and verified. With no map and one FMC; we had no choice but to believe the FMC was correct. The first officer and I have reviewed this over and over. We cannot figure out why this aircraft turned early.

Original NASA ASRS Text

Title: A B737-300 flying an RNAV departure with no moving map; no GPS and a single FMC had a track deviation at 1;000 FT but the navigation systems indicated normal tracking to the first waypoint while ATC saw it turn early.

Narrative: [We were] assigned an RNAV Departure and a standard transition. Departure was loaded into FMC and verified by both pilots at the gate. Runway 25R was also verified as the correct departure runway. Runway update was complete at the end of 25R and both NAV switches with placed in the down position. LNAV was selected at 400 FT AGL. At 1;000 FT AGL; LEGS page was selected on the single FMC. Our first waypoint; verified on LEGS page1; was 'magenta' and at the top left position. Command bars began to show a left turn for the waypoint. The wind at the airport was southerly in direction. The FMC showed a 235 heading to the waypoint. I immediately assumed a strong south wind and engaged the autopilot shortly after 1;000 FT. Departure ATC immediately said we made our left turn to early. All Flight Operations Manual procedures were followed and verified. With no MAP and one FMC; we had no choice but to believe the FMC was correct. The First Officer and I have reviewed this over and over. We cannot figure out why this aircraft turned early.

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 B737-300 flying an RNAV departure with no moving map; no GPS and a single FMC had a track deviation at 1;000 ft but the navigation systems indicated normal tracking to the first waypoint while ATC saw it turn early.