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ATSB Preliminary factual report on Boeing 747 electrical system event
19 February 2008

An ATSB preliminary factual report into an electrical system failure involving a Boeing 747-400 near Bangkok on 7 January 2008 indicates that the event was less serious than first reported.
The aircraft, with 346 passengers and 19 crew on board, was being operated on a scheduled service between London and Bangkok. When the aircraft was at about 21,000 feet on descent to Bangkok Airport, the customer service manager notified the flight crew that a substantial water leak had occurred in the forward galley. Over the following 12 to 13 minutes, cockpit indications showed a number of electrical bus and system failures that indicated alternating current (AC) buses, 1, 2 and 3 were not powered. The status of AC bus 4 appeared normal and some systems were powered by batteries.
The captains primary flight display, navigation display, and some other instruments were available in a degraded mode and the crew conducted an uneventful approach and landing in day visual meteorological conditions.
Post-flight inspections identified a minor water leak in the forward galley sink drain and that an ice drawer drain was blocked. That inspection also found cracks in a fibreglass drip shield located above an electrical component rack in the aircrafts main equipment centre, as well as evidence of dark liquid stains on the shield. Further inspection found that a ribbon heater on a drain line leading to the forward grey water drain mast was inoperative, and that a length of hose on the drain line at that location was split. (ATSB)