B747-400 crew had track deviation when the crew did not notice the FGS went from LNAV to heading.

Attributes
ACN	533742
Time
Date	200112
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : lin.vortac
State Reference	CA
Altitude	msl single value : 39500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zoa.artcc
Operator	common carrier : air carrier
Make Model Name	B747-400
Operating Under FAR Part	Part 121
Navigation In Use	other other vortac
Route In Use	departure sid : lin enroute : direct
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zoa.artcc
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 156 flight time total : 16000
ASRS Report	533742
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : far non adherence : company policies other anomaly other other spatial deviation
Independent Detector	atc equipment other atc equipment : radar other controllera
Resolutory Action	controller : separated traffic controller : issued alert controller : issued new clearance flight crew : overrode automation flight crew : returned to intended or assigned course
Miss Distance	horizontal : 27000 vertical : 1200
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

The first officer was doing the flying. We departed off of runway 1R sfo, SFO8-lin. The autoplt was engaged at about FL180. As we passed linden and climbing from FL390 for FL410, ZOA gave us direct wilson creek. I was working the CDU. We went through the verification procedure, 'how does that look?' first officer says, 'looks good' and I executed the procedure. LNAV was engaged and we were on our way to ilc. At about that time, we received an ACARS message. I was head down at that point, checking the message and during this time I felt the aircraft the rate of turn to the right. I looked at my pfd and we were no longer in LNAV -- we were in heading select and turning right of course. At this point, I advised the first officer to get the back around to the left towards ilc. That was when ZOA advised we had traffic off to the right at FL390 eastbound. The only thing that I can think that happened was, when the first officer rotated the heading bug around, he must have pushed it in and disengaged LNAV. We had the traffic visually and on TCASII. We received no TA or RA.

Original NASA ASRS Text

Title: B747-400 CREW HAD TRACK DEV WHEN THE CREW DID NOT NOTICE THE FGS WENT FROM LNAV TO HDG.

Narrative: THE FO WAS DOING THE FLYING. WE DEPARTED OFF OF RWY 1R SFO, SFO8-LIN. THE AUTOPLT WAS ENGAGED AT ABOUT FL180. AS WE PASSED LINDEN AND CLBING FROM FL390 FOR FL410, ZOA GAVE US DIRECT WILSON CREEK. I WAS WORKING THE CDU. WE WENT THROUGH THE VERIFICATION PROC, 'HOW DOES THAT LOOK?' FO SAYS, 'LOOKS GOOD' AND I EXECUTED THE PROC. LNAV WAS ENGAGED AND WE WERE ON OUR WAY TO ILC. AT ABOUT THAT TIME, WE RECEIVED AN ACARS MESSAGE. I WAS HEAD DOWN AT THAT POINT, CHKING THE MESSAGE AND DURING THIS TIME I FELT THE ACFT THE RATE OF TURN TO THE R. I LOOKED AT MY PFD AND WE WERE NO LONGER IN LNAV -- WE WERE IN HDG SELECT AND TURNING R OF COURSE. AT THIS POINT, I ADVISED THE FO TO GET THE BACK AROUND TO THE L TOWARDS ILC. THAT WAS WHEN ZOA ADVISED WE HAD TFC OFF TO THE R AT FL390 EBOUND. THE ONLY THING THAT I CAN THINK THAT HAPPENED WAS, WHEN THE FO ROTATED THE HDG BUG AROUND, HE MUST HAVE PUSHED IT IN AND DISENGAGED LNAV. WE HAD THE TFC VISUALLY AND ON TCASII. WE RECEIVED NO TA OR RA.

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.