Date: 201601
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Night
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Relief Pilot; Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: [We were] at FL350 approaching [an oceanic waypoint] when the flight deck relief crew observed a slight electrical odor initially believed to be coming from the first class galley ovens. Ovens were in use in the forward galley; but no electrical odor was observed in the galleys or passenger cabins. Relief pilots were on duty and directed the FAs to turn off the suspected oven; but the electrical odor continued to gradually increase in the cockpit and a light haze started to develop. The captain was on rest break when advised of the problem by the galley FA; and immediately returned to the flight deck. No odor; fumes; or smoke were observed by the captain outside the cockpit door or in the cabin.When entering the cockpit the Captain observed an acrid electrical odor and hazy smoke; called for the Smoke; Fire; Fumes Non-normal Checklist; and made the decision to divert to the nearest suitable airport. [ATC was advised] through Commercial Radio [patch]; and a turn initiated toward [a suitable airport]. Present position; fuel; and souls on board were provided with a request for emergency equipment to be standing by upon arrival. Dispatch was notified and [Maintenance] was brought on line to help troubleshoot. Upon completion of the checklist the odor and smoke continued; but ceased to increase in intensity. The Captain briefed the purser on the type of emergency; divert time; emergency equipment request; and to not prepare the cabin for evacuation; but to review emergency procedures. As [we] continued to divert; the odor and haze dissipated gradually; and conditions stabilized. Dispatch advised that [selected airport] was unsuitable and landing there would not be advisable due to tower closure and inability to contact emergency response personnel and equipment. The Captain and dispatcher made the decision to divert into [a different airport]; and ATC clearance was received. Emergency equipment was requested to be standing by upon arrival. The Captain advised FAs of the diversion; current status of the aircraft; and an announcement to the passengers was made. The source of the odor and smoke was unable to be identified; but [Maintenance] advised the crew that the aircraft had auto reported a failure of the cargo bulk ventilation fan. The crew dumped fuel down to MLW with [Maintenance] concurrence; completed the Diversion Checklist; and implemented CRM/TEM procedures. As the aircraft approached [the alternate airport] descending through 5;000 ft the pilots observed light electrical odor and haze return the cockpit and FAs reported an electrical odor within the first and business class cabins that was not previously observed. A normal approach was being flown when on short final [we] experienced a bird strike with no apparent damage noted. The aircraft landed safely and taxied to the gate. Emergency crews were asked to stand by and continue to monitor the aircraft until passengers were deplaned. Firefighters boarded the aircraft to perform a safety check and asked if the crew required further assistance. The Captain requested the firefighters supervise the opening of the bulk cargo door due to concern over possible overheat of the cargo bulk ventilation fan. The [inspection] was conducted with no evidence of smoke; fire; or fumes. Log entries were made by the flight crew and local maintenance was informed of the bulk cargo ventilation fan; the forward galley ovens; and the bird strike. Due to the early hour of arrival; only one mechanic was available to meet the flight. He said that he was unqualified and unable to address the cause of the electrical odor and smoke on the flight deck. The Captain called the Maintenance Controller and briefed him on details of the event. The Captain briefed the [Dispatch Manager] and Chief Pilot who were both working to secure rooms for the flight crew. Only one CSR was available to meet the flight. The cockpit and cabin crews did an outstanding job of accommodating passengers in the boarding area for two and a half hours with food; water; blankets; and pillows from the aircraft; and providing information as it became available while support teams were called. No hotel rooms were available due to [a] holiday and most passengers slept in the terminal area. Flight crews also did not have rooms locally and were transported to [a distant location] arriving there over four and a half hours after landing. The crew was given minimum rest and returned to the airport for continuation of the flight with the same aircraft. After maintenance worked to replace the cargo bulk ventilation fan and run [maintenance] protocol; they were unable to isolate the source of the acrid electrical odor and smoke. Maintenance removed aircraft from service and the flight was rescheduled for departure the following day with a replacement aircraft ferried. The flight departed the following afternoon and arrived without incident.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B777 flight crew reported that while enroute on a transoceanic flight they diverted to an alternate after noticing an acrid burning odor.