Date: 201602
Local time of day: 1201-1800
Location: ZZZZ.Airport, FO
Flight conditions: VMC
Light: Daylight
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
ATC / advisory: Center ZZZZ
Aircraft component: FMS/FMC
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Relief Pilot; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Time Pressure; Troubleshooting; Workload
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Became Reoriented; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: FMC selector Switch in L and POS REF 2 page L as primary. On track at FL360 we had a Dual FMC failure; shortly after making a RTE modification to the Arrival airport. We got the following malfunctions:  Amber Autopilot Caution followed by VNAV with a line through it. No magenta course line on either MAP with RTE 1; RTE 2; and the legs page operating normally. LNAV was engaged and in green. We tried to repair the loss of the route on our MAP by going to RTE2 to activate that. In the interim we went FLCH opened the speed window to M84. While trying to clean up RTE 2 we got 'Standby One' in the FMC scratch pad with the following indications: LNAV with a line through it; MAP inop on both MAPs; loss of all data in RTE 1. We went to HDG select to keep on course. Standby One lasted about 1 min; during that time we could not operate either FMC. After it went away our MAPs came back as well as the FMCs. We put our next point on the Fix page while waiting and when the FMCs came back put that point in RTE 1. Then rebuilt the rest of the RTE. LNAV was available again so we reengaged it. We fixed VNAV by putting in a Cruise Altitude and reloading the PERF page; then reengaging it. About 30 minutes after the event we got radar contact with ATC and reported that we had a loss of NAV for a short period of time. They confirmed we were on course. As far as I know we were on course the entire time even when in Heading select.


Second narrative: DUAL FMC failure following a few minutes after the PF executed an arrival transition correction. MCP with VNAV and amber line thru FMA followed shortly by both FMCs failing and map failure on both ND displays. We confirmed who was flying and who was working the problem; tried RTE 2; got a STANDBY ONE; prepared to do a DR (time and heading turn); recovered the box and manually entered the next 3 points which were in quick succession; approximately 40 miles from the FIR the situation became stable. The other pilot confirmed the points independently and we engaged LNAV and VNAV after entering a CRZ alt. ZFW and other parameters required reload. Once the next 2 points were accomplished and position was confirmed with ATC with VHF check in we loaded the remaining points; independently confirmed by the other pilot and called the Captain to the deck from break to review and confirm. We chose to wait until [entering our arrival country's] airspace to load the arrival or runway.


Synopsis: While at cruise on an oceanic route; B777 flight crew modified the destination airport's arrival in the FMC RTE 1 page. A dual FMC failure occurred shortly after; but the crew rebuilt the route and returned both FMCs to normal operation.