Electrical system event - Boeing 747-438, VH-OJM, 25 km north-north-west of Bangkok International Airport, Thailand, on 7 January 2008

On 7 January 2008, a Boeing Company 747-438 aircraft, registered VH-OJM, was being operated on a scheduled international regular public transport service between London, England and Bangkok, Thailand. The aircraft had 346 passengers and 19 crew on board, including four flight crew. On descent to Bangkok International Airport, the customer service manager notified the flight crew that a substantial water leak had occurred in the forward galley.

The cockpit indications progressively showed a number of electrical power-related malfunctions, and many of the aircraft's communication, navigation, monitoring and flight guidance systems were affected. A number of flight and navigation display and other instruments were available in degraded mode and the standby instruments and instrument landing system were also available. The aircraft's engines and hydraulic and pneumatic systems were largely unaffected and an approach was made to Bangkok in day visual meteorological conditions.

The investigation found the galley leak was from an overflowing drain after a drain line had been blocked with ice that formed due to an inoperable drain line heater. The water flowed forward and through a decompression panel into the aircraft's main equipment centre before leaking onto three of the aircraft's four generator control units, causing them to malfunction and shut down.

The investigation identified a number of safety issues in regard to the protection of aircraft systems from liquids, and other factors including the provision of information to flight crews. In response, the aircraft manufacturer and operator implemented a number of safety actions intended to prevent a recurrence. In addition, the United States Federal Aviation Administration issued a notice of proposed rulemaking to adopt a new airworthiness directive for certain 747-400 and 747-400D series aircraft to install improved water protection. The Australian Transport Safety Bureau has issued two safety recommendations and one safety advisory notice as a result of the investigation.