Aviation safety investigations & reports

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

Investigation number:
AO-2008-003
Status: Completed
Investigation completed

Summary

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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.

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Preliminary

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Preliminary report released 19 February 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.

At about 0837 UTC, while the aircraft was at about 21,000 feet on descent to Bangkok International Suvarnabhumi Airport, the customer service manager (CSM) notified the flight crew that a substantial water leak had occurred in the forward galley.

Between approximately 0840 and 0852, cockpit indications showed a number of electrical bus and system failures that indicated alternating current (AC) buses 2, 1 and 3 were not powered. The status of AC bus 4 appeared normal and some systems were powered by batteries.

The captain's primary flight display, navigation display, and some other instruments were available in a degraded mode. Standby instruments and the aircraft's instrument landing system were also available. The crew conducted an approach to runway 01 Right in day visual meteorological conditions and the aircraft landed at 0907.

On 11 January 2008, the aircraft manufacturer issued a Multi Operator Message to operators of 747 400 series aircraft, containing advice and instructions for the inspection and repair of main equipment centre drip shields. The manufacturer is preparing an inspection and repair alert service bulletin on the same subject that is scheduled for release by May 2008.

On 11 January 2008, the aircraft operator issued a Cabin Standing Order and a Flight Standing Order requiring cabin and flight crews to treat and report abnormal water accumulation in galley areas.

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Safety Issues

Go to AO-2008-003-SI-01 - Go to AO-2008-003-SI-02 - Go to AO-2008-003-SI-03 - Go to AO-2008-003-SI-04 - Go to AO-2008-003-SI-05 - Go to AO-2008-003-SI-06 - Go to AO-2008-003-SI-07 - Go to AO-2008-003-SI-08 - Go to AO-2008-003-SI-09 - Go to AO-2008-003-SI-10 - Go to AO-2008-003-SI-11 -

Maintenance processes did not identify or correct the deterioration of the dripshield

Maintenance processes did not identify or correct the deterioration of the drip shield.

Safety issue details
Issue number: AO-2008-003-SI-01
Who it affects: Operators of Boeing 747-400 aircraft
Status: Partially addressed

Floor sealing design

The location of the decompression panel and absence of cabin floor sealing above the main equipment centre increased the risk of liquid ingress into the aircraft’s electrical systems.

Safety issue details
Issue number: AO-2008-003-SI-02
Who it affects: Operators of Boeing 747-400 aircraft
Status: Partially addressed

Maintenance processes for corrosion in the generator control units

Maintenance processes did not identify or correct the corrosion in the generator control units.

Safety issue details
Issue number: AO-2008-003-SI-03
Who it affects: Operators of aircraft fitted with Hamilton Sundstrand Corporation generator or bus control units
Status: Adequately addressed

Maintenance processes for drain line heater

Maintenance processes did not identify or correct the inoperability of the forward drain line heater.

Safety issue details
Issue number: AO-2008-003-SI-04
Who it affects: Operators of Boeing 747-400 aircraft
Status: Adequately addressed

Maintenance processes for galley floor sealing

Maintenance processes did not identify or correct the deterioration of the galley floor sealing

Safety issue details
Issue number: AO-2008-003-SI-05
Who it affects: Operators of Boeing 747-400 aircraft
Status: Adequately addressed

Maintenance for drain lines

The galley drain operation and maintenance processes did not adequately prevent blockage and overflow of the aircraft’s drain lines.

Safety issue details
Issue number: AO-2008-003-SI-06
Who it affects: Operators of Boeing 747-400 aircraft
Status: Adequately addressed

Design of galley floor sealing

The floor sealing around the forward galley was not of sufficient extent to prevent liquids from passing through to the under floor area.

Safety issue details
Issue number: AO-2008-003-SI-07
Who it affects: Operators of Boeing 747-400 aircraft
Status: Adequately addressed

Operator’s documented design objectives

The aircraft operator’s documented design objectives did not explicitly require the protection of non-structural systems from liquid contact or ingress.

Safety issue details
Issue number: AO-2008-003-SI-08
Who it affects: Qantas Airways
Status: Adequately addressed

Flight crew quick reference handbook

The operator’s flight crew quick reference handbook did not include sufficient information for flight crew to manage the emergency.

Safety issue details
Issue number: AO-2008-003-SI-09
Who it affects: Operators of Boeing 747-400 aircraft
Status: Adequately addressed

Fluid protection design guidance

The United States Federal Aviation Administration regulations and associated guidance material did not fully address the potential harm to flight safety posed by liquid contamination of electrical system units in transport category aircraft.

 

Safety issue details
Issue number: AO-2008-003-SI-10
Who it affects: Manufacturers and operators of transport category aircraft
Status: Safety action pending

Battery discharge message priority design

The priority level of the battery discharge messages that were provided by the engine indicating and crew alerting system did not accurately reflect the risk presented by the battery discharge status.

Safety issue details
Issue number: AO-2008-003-SI-11
Who it affects: Operators of Boeing 747-400 aircraft
Status: Partially addressed
General details
Date: 07 January 2008   Investigation status: Completed  
Time: 0846 UTC   Investigation level: Complex - click for an explanation of investigation levels  
Location   (show map): 25 km NNW of Bangkok International Airport    
State: International   Occurrence type: Electrical system  
Release date: 13 December 2010   Occurrence class: Technical  
Report status: Final   Occurrence category: Serious Incident  
  Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer The Boeing Company  
Aircraft model 747  
Aircraft registration VH-OJM  
Serial number 25245  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point London Heathrow, UK  
Destination Bangkok, Thailand  
Last update 14 November 2018