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ATSB: investigation update on Boeing 747 depressurisation accident
17 November 2009

The Australian Transport Safety Bureau (ATSB) is continuing its rigorous and comprehensive examination of the circumstances surrounding the failure of an oxygen cylinder that led to the depressurisation of a Boeing 747 on a flight from Hong Kong to Melbourne in July 2008.

The ATSB’s second interim factual report on this accident indicates that to date there is no evidence of systemic safety problems with oxygen bottles of the type involved in the accident. Various tests have not been able to replicate the cylinder failure that initiated the accident.
The report provides details of the wide-ranging and ongoing technical examination of five oxygen cylinders obtained by the ATSB from the same manufacturing lot as the failed cylinder. The original cylinder was lost in the South China Sea in the course of the accident.

Analysis of the factual information and findings as to the factors that contributed to the accident remain the subject of ongoing work. Details will be included in the final report of the investigation.

To date, all pressure tests of the cylinders met or exceeded the relevant safety specifications, with recorded rupture pressures being over twice the maximum working pressure of the cylinders.

Other work is being carried out to determine the minimum size of mechanical flaws that could result in cylinder failure in service. The ongoing ATSB investigation will supplement that work with a program of rupture tests on cylinders that have had various sized ‘artificial’ flaws machined into the shell.

The ATSB expects to conclude the data gathering and analysis aspects of the investigation in early 2010, with a final report to follow. (ATSB)