Accident Boeing 737-809 B-18616,

ASN Wikibase Occurrence # 321897

Date:	Monday 20 August 2007
Time:	10:33
Type:	Boeing 737-809
Owner/operator:	China Airlines
Registration:	B-18616
MSN:	30175/1182
Year of manufacture:	2002
Total airframe hrs:	13664 hours
Engine model:	CFMI CFM56-7B26
Fatalities:	Fatalities: 0 / Occupants: 165
Aircraft damage:	Destroyed, written off
Category:	Accident
Location:	Okinawa-Naha Airport (OKA) - Japan
Phase:	Landing
Nature:	Passenger - Scheduled
Departure airport:	Taipei-Taiwan Taoyuan International Airport (TPE/RCTP)
Destination airport:	Okinawa-Naha Airport (OKA/ROAH)
Investigating agency:	JTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
China Airlines flight 120 departed Taipei at 08:14. It landed at Naha Airport (OKA) at 10:27 and taxied to the apron. Reaching the stand, ground engineers saw fuel gushing from an area near the no. 2 engine pylon. The pilot shut off the fuel supply to the engines after he was alerted by the ground engineer about the leak. Fuel from the leak flowed beneath the aircraft towards the no. 1 engine. The fuel ignited and the fire engulfed the airplane.
When all occupants had evacuated, a large explosion occurred in the centre of the airplane. The airplane burned out completely.

PROBABLE CAUSE: "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.
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detached from the aft end of the above-mentioned inboard main track fell off into the track can, and when the slat was retracted, the assembly was pressed by the track against the track can and punctured it.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."

Accident investigation:


Investigating agency:	JTSB
Report number:	AA2009-7
Status:	Investigation completed
Duration:	2 years
Download report:	Final report

Sources:

SKYbrary
China Airlines plane goes up in flames at Naha airport; nobody hurt (Japan Today, 20-8-2007)
Jet fuel gushed from plane on landing (Asahi Shimbun, 22-8-2007)
Investigators find hole in fuel tank of plane that exploded in Japan airport (AP, 23-8-2007)

Location

Images:

photo (c) Thomas Mitchell; Okinawa-Naha Airport (OKA/ROAH); 20 August 2007; (CC:by-sa)