The Australian Transport Safety Bureau (ATSB) has concluded that the rupture of a Qantas Boeing 747-400's emergency oxygen cylinder in July 2008 was an "unusual" incident, and is unable to identify any particular reason for the failure.
The aircraft, which was carrying 369 passengers and crew, was 55 minutes into a flight to Melbourne from Hong Kong and cruising at 29,000ft when it rapidly depressurised following the rupture in the forward cargo hold. The crew made an emergency descent to 10,000ft, and landed safely at Manila's Ninoy Aquino International Airport without any injuries.
Investigations found that the No 4 oxygen cylinder along the right side of the forward cargo hold had burst. It had ruptured the adjacent fuselage wall, propelled upwards and punctured the cabin floor, and hit the frame and handle of the R2 door and the overhead cabin panelling. No part of the cylinder, apart from the valve assembly, has been recovered and is believed to have been lost during depressurisation.
"It was evident that the cylinder had failed by bursting through, or around the base - allowing the release of pressurised contents to project it vertically upwards," says the ATSB. It adds that it closely studied the cylinder type and reviewed all possible failure scenarios, and conducted an evaluation of other cylinders from the same production batch and of the type in general
However, it could not find any evidence that the cylinder may have contained a defect or flaw that led to the failure. Investigations confirm that the cylinder was "fit-for-purpose", and that there was nothing to suggest that they could be a threat to the safety or airworthiness of the design, it adds.
"In summary, the investigation found that the manner of cylinder failure was unusual and implicated the presence of a defect, or action of a mechanism that directly led to the rupture event. However, despite the extensive exploration of the available evidence and the study of multiple hypothetical scenarios, the investigation was unable to identify any particular factor or factors that could, with any degree of probability, be associated with the cylinder failure event," concludes the ATSB.