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An electrical systems failure onboard a Boeing 747 aircraft near Bangkok, Thailand has prompted extensive safety actions from Qantas, Boeing and the US Federal Aviation Administration.

On 7 January 2008, the aircraft lost electrical power to many of its onboard systems as a result of overflowing drain water entering generator control units that control the distribution of electrical power.

In response to the event and the ATSB investigation, Qantas, Boeing and the US Federal Aviation Administration (FAA) have implemented a number of safety actions to prevent a recurrence. These actions include reinforcing protective 'dripshields' above electrical equipment, improving maintenance practices and pilot training and installing advanced standby flight instruments to Qantas 747 aircraft.

In addition, the generator control unit manufacturer, Hamilton Sundstrand, has increased its monitoring of returned units for signs of liquid contamination.

Despite these safety actions, the ATSB found that the FAA's regulatory and guidance information does not fully address the potential harm to flight safety posed by liquid contamination of electrical system units in transport aircraft. As well, the information provided to 747-400 flight crews regarding standby power operations is limited. The ATSB has made recommendations to the US FAA and Boeing to address those safety issues.

The ATSB has also released a Safety Advisory Notice reminding operators and flight crews about the need to respond immediately to battery discharge alerts.

The ATSB investigation report, released today, describes how three of the aircraft's four main electrical power supplies stopped operating after water entered three of the aircraft's generator control units. A drain line heater had failed, causing an ice blockage which led to the drain line overflowing in the galley. The water flowed through a gap in the aircraft's floor, then through a dripshield and into the generator control unit.

This affected cabin lighting and many of the aircraft's communication, navigation, instrumentation and flight guidance systems, including the autopilot. Many aircraft systems were subsequently powered by the aircraft's emergency batteries.

The aircraft's engines, hydraulic system, and pneumatic systems were largely unaffected and it landed safely at Bangkok shortly afterwards. None of the 346 passengers and 19 crew were injured.




 
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Last update 01 April 2011