Date: 201807
Local time of day: 1201-1800
Location: EGGX.ARTCC, FO
Flight conditions: VMC
Aircraft: B777-200
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
ATC / advisory: Center EGGX
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Human-Machine Interface; Situational Awareness; Troubleshooting
Second reporter function: Pilot Not Flying; Captain
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Aircraft Equipment Problem Dissipated; Flight Crew Diverted; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: At 36;000 feet; the 'aft cargo warning' message appeared on the EICAS along with the fire bell. I was flying in the right seat and the FB (Relief Pilot) was pilot monitoring in the left seat. We assessed the warning and immediately ran the ECL for the fire. We accomplished all steps of the ECL which included arming and discharging the extinguishing agent. We then began the procedure for leaving the NAT track. I flew and the FB called Shanwick and also the Captain; who had been in crew rest in the cabin for approximately 20-30 minutes. Before the Captain left he had instructed me that if anything abnormal arose that required a divert; to run the ECL; start the off-track procedures and then call him; which we did. The Captain also told me that whatever our closest divert was and that would be the best choice.This briefing helped me make a quick decision where to divert. When the Captain returned to the flight; he and the FB continued to work the clearance to the divert airport and assure traffic separation while I flew the aircraft. We were cleared direct by oceanic control over HF and proceeded that way. After a minute or two the fire indication went away and temperatures in the cargo appeared normal on the air synoptic. The captain then briefed the flight attendants fully and made a pa to the passengers about the necessary divert. We flew a normal descent and ILS approach and landing. We had informed approach and tower that we would stop on the runway for a FLIR inspection by the ARFF (Airport Rescue and Firefighting) team. We did that and were given the all clear. We then taxied to the hot cargo ramp where we shutdown the aircraft and deplaned passengers and crew down air stairs to waiting busses. The captain and ARFF team member did a final walk through of the aircraft to make sure everyone was accounted for. The flying Captain and FB both did an outstanding job during this event. True professionals in every way!Something in the smoke detection system sensed a possible fire.


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


Synopsis: B777-200 flight crew reported a fire warning light and diverted to the nearest suitable airport.