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The Australian Transport Safety Bureau has released an interim factual report on its investigation into the Qantas Boeing 747 depressurisation event that occurred 475 km north-west of Manila, Philippines on 25 July 2008.

The ATSB's preliminary report, released in August 2008, provided details on the circumstances of the accident, in which a passenger oxygen cylinder (the number-4 cylinder) failed and ruptured the aircraft's fuselage, while the aircraft was cruising at 29,000 ft on a scheduled passenger flight (QF30) from Hong Kong to Melbourne. As a result of the depressurisation, the flight crew diverted the aircraft to Ninoy Aquino International Airport, Manila, where an uneventful visual approach and landing was made.

There were no major injuries, although there were reports of ear pain and discomfort associated with the rapid depressurisation, including some faintness and light-headedness. There was also evidence that showed that a large portion of the failed oxygen cylinder had been propelled upward through the cabin floor, impacting with the R2 door and the overhead ceiling panels, before exiting the aircraft through the fuselage rupture.

The interim factual report released today contains information on the progress, and future direction, of the investigation. Analysis of the factual information and findings as to the factors that contributed to the accident are subject to ongoing work and will be included in the final report.

The investigation has determined that, despite the damage to the aircraft's passenger oxygen system caused by the oxygen cylinder failure, the system would have continued to operate for approximately 65 minutes following the depressurisation event. Passenger oxygen was only required for about 5 minutes during the period between the depressurisation event and when the aircraft reached an altitude of 10,000 ft.

Tests have revealed no evidence of an external explosive event or the use of explosive materials around the rupture area. The oxygen valve from the number-4 cylinder, which was the only item of physical evidence recovered from the cylinder, has also been closely examined, with no evidence to suggest that an oxygen-promoted fire or an overpressure event had contributed to the cylinder failure.

No significant maintenance difficulties had been experienced with the passenger oxygen system prior to the occurrence. Investigators visited the Qantas Sydney Jet Base oxygen workshop, where the servicing and replenishment of all Qantas oxygen cylinders is performed. The inspections did not identify any significant issues or deviations from documented practice that had the potential to affect the integrity of the cylinder-valve assemblies.

The ATSB obtained two samples of the gaseous oxygen that was used to fill the number-4 cylinder. These samples have been analysed and compared against the required specification for aviators breathing oxygen. No anomalies were identified that would have contributed to this event.

The remaining cylinders from QF30, together with five other cylinders from the same manufacturing batch lot as the number-4 cylinder are being physically examined for evidence of any deficiencies or deviations from the certified design. This will help further understand the cylinder failure event (because the number-4 cylinder was not recovered and is presumably lying on the bottom of the South China Sea).

Special computer modelling and analysis of the oxygen cylinder design will also provide an enhanced understanding of the cylinder shell stresses, and an assessment of the critical flaw size required to produce an uncontrolled cylinder failure.

Several cylinders from the number-4 batch have been destructively tested and the shell material mechanical and metallurgical properties established. The results are being used to establish the fundamental strength levels of the cylinder type, and whether or not the properties of the batch meet the certified design requirements. No major anomalies have been observed at this stage.

Hydraulic and pneumatic testing of several 'batch' cylinders is also planned. The pneumatic testing will provide further understanding of the mechanism and characteristics of a cylinder failure at elevated pressures. In addition to the pneumatic tests, both cyclic and static hydraulic pressure tests will be performed on select cylinders to establish their performance against the certified design requirements.

The investigation will also continue to examine the serviceability and functionality of the cabin oxygen apparatus and other cabin safety equipment, cabin crew actions, and passenger actions and problems. The cabin safety / survival factors investigation will employ the information gathered from the operating crew interviews and passenger surveys, to review the cabin crew procedures and determine whether any improvements or changes to those procedures would enhance safety.

The ATSB has received survey responses from approximately 47% of the aircraft passengers. Passengers who have received a survey, but have not yet responded are encouraged to do so. Replacement surveys are also available for those that may have misplaced or did not receive the original documents please provide an email or postal address to the ATSB (aviation.investigation@atsb.gov.au) or phone +61 26257 4150 (from overseas) or 1800 020 616 (within Australia).

Safety actions arising from the occurrence commenced on 27 July 2008 (2 days after the event), with the operator completing a fleet-wide program of detailed visual inspections of its Boeing 747 oxygen system installations. The operator has completed a preliminary internal review of the event, addressing the crew and passenger response, the emergency passenger oxygen system operation, supplementary passenger oxygen requirements, and the functionality of the depressurisation emergency announcement system operation.� Some cabin crew procedural changes have also been implemented.

The ATSB has published two safety advisory notices recommending that operators and maintainers ensure all procedures and activities meet the appropriate requirements and are best practice. The ATSB has also published two Research and Analysis reports providing information for passengers and cabin crew in the event of an aircraft depressurisation.

The ATSB expects to release a final report into this accident towards the end of 2009. However, the ATSB will immediately bring any critical or significant safety issue(s)s to the attention of the relevant organisations best placed to address them, should any such issues arise. The ATSB will also publish details of any such issue(s).

Media contact: 1800 020 616
 
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Last update 01 April 2011