B777-200 crew reports momentary course deviation on north atlantic random track.

Attributes
ACN	725081
Time
Date	200701
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : czqx.artcc
State Reference	NF
Altitude	msl single value : 34000
Aircraft 1
Controlling Facilities	artcc : czqx.artcc
Operator	common carrier : air carrier
Make Model Name	B777-200
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : relief pilot
Experience	flight time last 90 days : 160 flight time total : 18000 flight time type : 5000
ASRS Report	725081
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 210 flight time total : 12000
ASRS Report	725077
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : returned to intended or assigned course flight crew : overcame equipment problem
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Ambiguous

Narrative:

At the time of the incident; the captain was on rest break. I was acting as relief pilot in the left seat. On a random nat route over the atlantic; approximately 58 NM west of n57w040; the aircraft began an immediate right turn towards north; off the track while flying in LNAV. The turn was stopped after approximately 25 degrees of deviation by selecting heading mode. A 50 degree intercept course back to the nat was immediately initiated. We then noticed our next waypoint on the route (n58w050) had dropped out of the database. We reinstalled the coordinates; verified the course to the coordinates against our fpf and rejoined the track in LNAV. During this incident our magenta course line remained on screen as did our 1 degree offset line to the right. No further anomalies were encountered and we briefed the captain of the incident when he returned off break. There was not a gross deviation during the incident -- the other first officer and myself both agreed that we remained within 6-10 NM of the assigned nat. Winds at FL340 were prevailing from approximately 180 degrees at +130 KTS at the time of the incident. Maintenance control was notified immediately as well as our dispatcher. After landing; the captain contacted the on-duty flight operations supervisor to advise him of the incident.

Original NASA ASRS Text

Title: B777-200 CREW REPORTS MOMENTARY COURSE DEVIATION ON NORTH ATLANTIC RANDOM TRACK.

Narrative: AT THE TIME OF THE INCIDENT; THE CAPT WAS ON REST BREAK. I WAS ACTING AS RELIEF PLT IN THE L SEAT. ON A RANDOM NAT RTE OVER THE ATLANTIC; APPROX 58 NM W OF N57W040; THE ACFT BEGAN AN IMMEDIATE R TURN TOWARDS N; OFF THE TRACK WHILE FLYING IN LNAV. THE TURN WAS STOPPED AFTER APPROX 25 DEGS OF DEV BY SELECTING HDG MODE. A 50 DEG INTERCEPT COURSE BACK TO THE NAT WAS IMMEDIATELY INITIATED. WE THEN NOTICED OUR NEXT WAYPOINT ON THE RTE (N58W050) HAD DROPPED OUT OF THE DATABASE. WE REINSTALLED THE COORDINATES; VERIFIED THE COURSE TO THE COORDINATES AGAINST OUR FPF AND REJOINED THE TRACK IN LNAV. DURING THIS INCIDENT OUR MAGENTA COURSE LINE REMAINED ON SCREEN AS DID OUR 1 DEG OFFSET LINE TO THE R. NO FURTHER ANOMALIES WERE ENCOUNTERED AND WE BRIEFED THE CAPT OF THE INCIDENT WHEN HE RETURNED OFF BREAK. THERE WAS NOT A GROSS DEV DURING THE INCIDENT -- THE OTHER FO AND MYSELF BOTH AGREED THAT WE REMAINED WITHIN 6-10 NM OF THE ASSIGNED NAT. WINDS AT FL340 WERE PREVAILING FROM APPROX 180 DEGS AT +130 KTS AT THE TIME OF THE INCIDENT. MAINT CTL WAS NOTIFIED IMMEDIATELY AS WELL AS OUR DISPATCHER. AFTER LNDG; THE CAPT CONTACTED THE ON-DUTY FLT OPS SUPVR TO ADVISE HIM OF THE INCIDENT.

Data retrieved from NASA's ASRS site as of January 2009 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.