On July 30 2008, a Boeing 777-200 being operated by Vietnam Airlines on a scheduled passenger flight landed at Narita in daylight and normal visibility and shortly afterwards experienced a right engine fire warning with the appropriate crew response following. Subsequently, after the aircraft had arrived at the parking stand and all passengers and crewmembers had left the aircraft, the right engine caught fire again and this fire was extinguished by the Airport RFFS who were already in attendance. There were no injuries and the aircraft sustained only minor damage.
An Investigation was carried out by the Japan TSB. The Investigation noted that in the cruise en route to Tokyo, the flight crew had observed cautions in respect of the right hand engine Fire Loop and in respect of ‘overheat circuit R2’ but there were no other indications and it was concluded that something was probably faulty in the engine fire sensing system.
The subsequent right hand engine fire after landing was indicated by a fire warning and it was concluded that fuel had leaked from the engine 2 fuel supply hose coupling and that it was highly probable that the leaking fuel would have spread in the area of the junction box during taxiing, which had then ignited. The time when the fuel started to leak could not be determined but it was considered highly probable that it was during the preceding flight and that the flow of air in flight made it difficult for the leaking fuel to ignite, whereas when the aircraft moved in a tailwind on the taxiway after landing and the flow of air inside the engine had become slower, this would have provided a scenario more favourable to ignition.
The fire after the aircraft had parked was considered likely to have been enabled through the opening of the fuel and hydraulic fluid shutoff valves by maintenance personnel when they moved the right hand engine Fire Handle back to the original position in preparation for motoring the engine to stop the white smoke. Fuel or hydraulic fluid could then leak out and ignited due to the heat from hot spots in the engine. The fact that white smoke continued to issue from the engine after the first fire despite the pulled Fire Handle was considered likely to have been a result of hydraulic fluid leaking from hoses that had been damaged by the initial fire.
It was found that the aircraft had been on ‘C’ Check between 2 July and 23 July 2008 and that this had included removal and reinstallation of the right hand engine fuel supply hose as part of the fuel supply line inspection with the O-ring in the fuel supply hose being replaced during the fuel system inspection.
It was determined that the Probable Cause of the incident was “that fuel leaked from the fuel supply hose of the right engine while the aircraft was taxiing after landing and that the leaking fuel caught fire… It is considered possible that fuel leaked due to a gap in the O-ring that was created when the O-ring was pinched and severed during installation of the fuel supply hose. It is considered possible that the installation of the O-ring which was smaller in size and easily loosened, as well as the non-use of lubricant, contributed to the pinching.“
The Final Report of the Investigation was published on 23 April 2010: JTSB - AI2010-3
It contained one Safety Recommendation directed at the aircraft manufacturer:
“Since the Aircraft Maintenance Manual (AMM 73-11-08-400-801) for the installation of the fuel supply hose on the Boeing 777-200 had not included a description regarding application of lubricant to the O-ring during its installation, the manufacturer of the Aircraft issued a temporary revision to the manual, dated May 6, 2009. Permanent measures to be taken by the manufacturer of the Aircraft against the recurrence of similar serious incidents are expected to be decided after completion of this investigation by the JTSB.”