Air France B772 near Seoul on Mar 14th 2012, engine failure

An Air France Boeing 777-200 freighter, registration F-GUOB performing freight flight AF-6775 from Seoul (South Korea) to Paris Charles de Gaulle (France) with 3 crew, was climbing through about 9,600 feet out of Seoul about 5 minutes into the flight when the crew received indication of a thrust anomaly on the right hand engine (GE90). The crew declared PAN, shut the engine down, dumped fuel and returned to Seoul's Incheon Airport. On final approach to runway 34 the crew received indication the right hand engine had failed and shut down, declared Mayday and continued the landing for a safe touch down and roll out.

South Korea's ARAIB released their final report in Korean concluding the probable cause of the incident was:

the fuel pump was contaminated with metal fragments inside the interstage fuel strainer and the fuel control unit (HMU) did not work properly preventing the engine to reach the pilot commanded thrust output.

The ARAIB reported that the fuel pump had been swapped the previous day after the aircraft had experienced a fuel leak on the flight inbound to Seoul. A fuel pump, that had not been used in the 6 weeks prior to the occurrence, was mounted on the aircraft. A post occurrence inspection revealed a bolt had wedged inside the interstage strainer. Laboratory analysis identified the bolt as being identical with the bolts to be used for mounting the fuel pump.

The pressure differential valve, that should have opened to enable the fuel bypass the blocked main fuel feed and thus enable to fuel pump to supply fuel to the engine without restriction, was also found obstructed with metal fragments which prevented the valve to operate.

The bolt, while becoming wedged within the interstage strainer caused a hole which released metal fragments into the fuel pump's bearings and gearings, which ultimately resulted in the engine failure and shut down when the cog wheels became sufficiently deteriorated as result of the foreign objects.

Fuel system (Graphics: ARAIB):

Interstage strainer, bolt and hole (Graphics: ARAIB):

Bearing and gearing (Graphics: ARAIB):