Australian investigators are continuing to carry out oxygen cylinder tests as part of their probe into the in-flight explosion of a cylinder on a Qantas Airways Boeing 747-400 last year.
The Australian Transport Safety Bureau (ATSB) has been assessing design properties of emergency oxygen cylinders since the 25 July incident, which occurred as the 747-400 was operating as flight QF30 from Hong Kong to Melbourne.
No serious injuries occurred in the incident although a large section of the aircraft's fuselage separated, resulting in a depressurisation and emergency landing in Manila.
Investigators determined that the depressurisation occurred after a passenger oxygen cylinder exploded and ruptured the aircraft's fuselage when the 747 was cruising at 29,000ft (8,840m).
The ATSB says in an interim factual report released today that the remaining cylinders recovered from the aircraft together with five others from the same manufacturing batch lot are still being physically examined for evidence of deficiencies or deviations from the certified design.
It also says computer modelling and analysis of the oxygen cylinder design will be carried out to "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 same manufacturing batch have already been destructively tested and the results are being used to establish fundamental strength levels, says the ATSB.
In addition, hydraulic and pneumatic testing of several more cylinders is planned.
"The pneumatic testing will provide further understanding of the mechanism and characteristics of a cylinder failure at elevated pressures," says the ATSB.
"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 ATSB says it expects to release a final report late this year.