Australian safety regulators have called for US regulations to address the potential risk caused by liquid contamination of aircraft electrical systems, following an investigation into a 2008 Qantas Airways Boeing 747 power loss incident.
The Australian Transport Safety Bureau (ATSB), which released its final report into the incident today, also urged Boeing to update its handbook for 747 flight crews to help them make the right decisions when working with an electrical power loss.
In the 7 January 2008 incident, the Qantas 747 registration VH-OJM, experienced an electrical power loss while on approach to Bangkok after a flight from London. This followed the discovery of a "substantial water leak" in the forward galley.
The aircraft landed safely, and none of the 346 passengers and 19 crew on board were injured.
Investigations found that the leak was from an overflowing drain after a drain line was blocked with ice that had formed due to an "inoperable drain line heater", says the ATSB. "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 units, causing them to malfunction and shut down."
Maintenance processes did not identify or correct the drain line heater and the deterioration of the dripshield, says the ATSB. It also identified the absence of cabin floor sealing above the main equipment centre as a factor that increased the risk of liquid seeping into the aircraft's electrical systems.
As a result of the incident, Boeing issued a service bulletin to operators to modify 747-400 dripshields, as well as instructions on inspecting and repairing the equipment. The aircraft manufacturer is also studying ways to improve the floor sealing in 747 aircraft, says the ATSB.
Qantas reviewed its maintenance processes, stepped up inspections of dripshields on its fleet and also made modifications to its aircraft to prevent similar incidents.
While the ATSB is satisfied with most of the safety actions taken after the incident, it says current US Federal Aviation Administration regulations do not "fully address the potential harm to flight safety posed by liquid contamination of electrical system units in transport category aircraft".
"The ATSB recommends that the US FAA take safety action to address this safety issue," it adds.
It also called on Boeing to provide more information in its 747 reference handbook for crew to refer to in the event of having to manage operations on standby power.
"There is currently limited assurance that 747-400 flight crews would be aware of the expected duration of available battery power or of the possible need to expedite appropriate actions such as aircraft diversion that should be undertaken in the event of abnormal or unexpected battery discharge," says the ATSB.
It recommended "the inclusion of a note or caution associated with the battery discharge message entry" in the handbook to alert flight crews to a restricted battery life.