Japan's Transport Safety Board (JTSB) has confirmed that a fire, which destroyed a China Airlines (CAL) Boeing 737-800 in August 2007, was due to maintenance error.
It has also recommended in its report that regulators improve the wording in the service letters and bulletins to prevent such accidents from recurring.
The JTSB found that a bolt, which was used to support a pylon of a slat on the leading edge of the right wing, fell off and pierced the fuel tank. As a result, fuel leaked out and ignited, resulting in the fire.
The accident occurred on while the 737-800 was at the terminal at Naha airport in Japan.
"It is considered highly probable that during maintenance works... carried out one and a half months prior to the accident ...the washer on the nut side of the assembly fell off", which meant the bolt was only held by a nut, says the JTSB.
It also says there was a problem with the design because without the washer, the nut was unable to stop the bolt from falling off.
In its investigation report, the JTSB has made recommendations to the US FAA and the Taiwan Civil Aeronautics Administration.
"When preparing maintenance job instructions for airlines such as service letters and bulletins, the scope of the jobs should be clearly defined and the working conditions and environments including accessibilities to the job areas should be appropriately evaluated in order to prevent maintenance errors," it says.
Following the accident, Boeing changed the design of the nut to limit the likelihood it will detach from the bolt.
Source: Air Transport Intelligence news
