sentences:  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.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detached from the aft end of the above-mentioned inboard main track fell off into the track can, and when the slat was retracted, the assembly was pressed by the track against the track can and punctured it.With regard to the cause of the detachment of the downstop assembly, it is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 was omitted, following which the downstop on the nut side of the assembly fell off and then the downstop assembly eventually fell off the track.