On 20 August 2007, as a Boeing 737-800 being operated by China Airlines on a scheduled passenger flight arrived on the designated nose-in parking stand at destination Naha, Japan in daylight and normal visibility, fuel began to leak from the right wing near to the engine pod and ignited. An evacuation was quickly initiated and all 165 occupants including 8 crew members were able to leave the aircraft before it was engulfed by the fire, which spread rapidly and led to the destruction of the aircraft and major damage to the apron surface. As the stand was not adjacent to the terminal and not served by an air bridge, there was no damage to structures. All occupants had left the aircraft before the Airport RFFS arrived at the scene.
An Investigation into the Accident was carried out by the Japan Transport Safety Board (JTSB). This established that the fuel leak had occurred from the right hand wing fuel tank after a hole had been punctured in the wing track can that housed the inboard main track of the No. 5 slat when the flaps and slats were retracted during the taxi in at Naha.
Ignition of the fuel was considered to have been the result of some of it coming into contact with the hot engine exhaust close by and the fire was then fed by fuel pooling on the apron below the leak source.
Flight crew awareness of a fire was first achieved by a ground crew communication which described only an ‘engine fire’ as the engines were being shut down on the gate for which there were no corresponding flight deck indications.
The JTSB published their Final Report on 28 August 2009 which states under ‘Probable Cause’ that:
“It is considered highly probable that this accident occurred through the following causal chain: When the Aircraft retracted the slats after landing at Naha Airport, the track can that housed the inboard main track of the No. 5 slat on the right wing was punctured, creating a hole. Fuel leaked out through the hole, reaching the outside of the wing. A fire started when the leaked fuel came into contact with high-temperature areas on the right engine after the Aircraft stopped in its assigned spot, and the Aircraft burned out after several explosions.
Damaged Inner Track Can of Slat Nr 5
With regard to the cause of the puncture in the track can, it is certain that the downstop assembly having detached from the aft end of the above-mentioned inboard main track fell off into the track can, and when the slat was retracted, the assembly was pressed by the track against the track can and punctured it. With regard to the cause of the detachment of the downstop assembly, it is considered highly probable that during the maintenance works for preventing the nut from loosening, which the Company carried out on the downstop assembly about one and a half months prior to the accident based on the Service Letter from the manufacturer of the Aircraft, the washer on the nut side of the assembly fell off, following which the downstop on the nut side of the assembly fell off and then the downstop assembly eventually fell off the track.
It is considered highly probable that a factor contributing to the detachment of the downstop assembly was the design of the downstop assembly, which was unable to prevent the assembly from falling off if the washer is not installed. With regard to the detachment of the washer, it is considered probable that the following factors contributed to this:
- Despite the fact that the nut was in a location difficult to access during the maintenance works, neither the manufacturer of the Aircraft nor the Company had paid sufficient attention to this when preparing the Service Letter and Engineering Order job card, respectively.
- Also neither the maintenance operator nor the job supervisor reported the difficulty of the job to the one who had ordered the job.”
As a consequence, and taking account of safety actions which had occurred during the course of the Investigation, two Safety Recommendations were included in the Final Report:
- Preparation of Maintenance Job Instructions - The Japan Transport Safety Board recommends the Federal Aviation Administration of the United States of America to supervise the Boeing Company, the manufacturer of the Aircraft, to take the following actions:
- When preparing maintenance job instructions for airlines such as Service Letters/Bulletins, the scopes of jobs should be clearly defined and the working conditions and environments including accessibilities to job areas should be appropriately evaluated in order to prevent maintenance errors.
- Planning and Implementation of Maintenance Jobs - The Japan Transport Safety Board recommends the Civil Aeronautics Administration of Taiwan to supervise China Airlines to take the following actions:
- When planning and implementing maintenance jobs, the scopes of jobs should be fully ascertained and the working conditions and environments should be appropriately evaluated, and the countermeasures to prevent maintenance errors including the actions taken in 2009 against the recurrence of this accident should be steadfastly implemented and enhanced.