Date: 201511
Local time of day: 0001-0600
Location: ZZZZ.Airport, FO
Flight conditions: VMC
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Human factors: Troubleshooting; Workload; Time Pressure; Situational Awareness
Second reporter function: Captain; Pilot Not Flying
Anomaly: Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Air Traffic Control Issued New Clearance; Flight Crew Landed in Emergency Condition; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Diverted
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: A B777; flying at FL310; experienced a 'Fire Cargo Aft' Warning. The checklist was accomplished and the fire bottles were discharged. The fire indication remained. A divert was executed the nearest suitable airport; which was ZZZZ. Fuel dump was commenced using 'Fuel Jettison' checklist as the aircraft weight was at 701;000 lbs and the max landing weight of aircraft is 575;000 lbs. Approaching ZZZZ; control advised that the [airport] would not be open for several minutes and to expect 15 min of holding. At that time we diverted to ZZZZ1. At about this time the fire indication went away. Fuel dump was stopped at  10;000 feet and an over weight landing was completed safely at ZZZZ1 at 589;000 lbs. The aircraft was stopped on the runway and fire crews drove around the aircraft confirmed no obvious fire to fight. The aircraft was shut down with the APU running. 10 minutes after shutting down the aircraft the 'Fire Cargo Aft' alert came on again. The aircraft was completely de-powered and the crew exited via crew stairs that were brought to the aircraft. At no time did the crew notice indication of smoke or fumes. Suspect undeclared [Hazmat] caused cargo fire.


Second narrative: [In flight] we received a master warning with EICAS display 'cargo fire aft'. I was Pilot Monitoring and accomplish the 'cargo fire aft' checklist which included discharging the fire bottles. The fire warning remained active. I [told ARTCC] and initiated a left turn towards ZZZZ which was the closest airport. We initiated fuel jettison (FL300). The airport was closed but they were trying to open it for us. As we approached ZZZZ we were informed that it would take another 15 minutes to open the airport -- which was IFR at the time. We elected to proceed to ZZZZ1. Fuel jettison was terminated at approximately 10;000 feet before crossing the shoreline. During the approach the fire warning extinguished. I assumed control of the aircraft and accomplished an overweight landing [in ZZZZ1] at approximately 589;000 lbs. We stopped on the runway for inspection and taxied to the gate. During our post fight the fire warning reoccurred. We depowered the aircraft and evacuated via stairs. We were unsuccessful in trying to convince the fire fighters to open the cargo door immediately to check for fire. Language problems were an issue.


Synopsis: The crew of this Boeing 777 cargo aircraft reported experiencing a 'Fire Cargo Aft' warning while at cruise altitude. They accomplished all appropriate checklists; coordinated a clearance with Air Traffic Control; and successfully diverted to a suitable airfield.