"The ATSB says investigations are continuing into the functioning of the cabin oxygen masks and into the design and manufacture of the failed oxygen cylinder."
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Not disclosed in this report is the reason why the oxygen bottle may have failed. I cannot believe the ATSB is that dumb. In fact they've been unable to come to any conclusions. However a very simple conjecture can address the distinct probabilities.
Every aircraft type I've ever flown has had a minimum oxygen pressure below which you should never allow the contents to drop. The reason for that is simply that, at low pressures (say <300psi) moisture then readily gathers inside the bottle and it can then corrode undetected from the inside out (recalling that the lower and outer part of this bottle failed - where the water would tend to gather on the fuselage-mounted and slightly inclined cylinder's outermost wall). The exploding bottle eventually completed its jet-about final fling and departed via a final trickle-down through the hole in VH-OJK's fuselage - so no proof of this having been a corrosion incident is now available (except perhaps in other bottles of the same and "other" fleet systems). If a bottle (or "bottles" as part of a plumbed-together system) ever drops below that min pressure, it (they) has to be removed, evacuated, refilled and re-installed or kept (full) in storage as a spare. In consequence, engineers are usually careful not to allow oxygen systems to drop to those levels (unless it's within a closed/plumbed and therefore humidity-controlled environment). You cannot tell whether (or not) an oxygen bottle or system has been allowed to accumulate moisture. There are no in-tank dessicants and no water-collecting low points and drainage ports as in a pitot-static system. Compared to aviation's dehumidified dry breathing oxygen, medical oxygen is humidified and therefore hospital oxygen bottles are regularly evacuated and drained before being refilled.
My theory is that at some stage some systems (including this system on VH-OJK) was allowed to drop to a low or zero pressure and accumulated water via atmospheric moisture ingress and that it's been corroding at an accelerated rate over time. When and why might this have happened? Well you may recall that a year or so ago (see article below) QANTAS was found to have been mistakenly filling/topping off oxygen systems with Nitrogen over a lengthy period - due to a task delegation to a lowly qualified engineer who changed out a connector and enabled this alarming mistake to occur - not only to QANTAS aircraft but to a whole bunch of transient international aircraft that they (QANTAS) were in-transit servicing contractors for. Nitrogen, unlike dry breathing oxygen, is not really a zero humidity-controlled gas. It's normally used only for servicing tyres and oleos etc.
Read the thread below and judge for yourself. The nitrogen fiasco was uncovered in Dec 2007 but had been going on long before that. How long (after being emptied and refilled with guaranteed pure oxygen - but not water-checked) does it take corrosion to weaken a tank in a pressurized oxygen rich (and nitrogenized) H2O environment? The corrosion rate is about 5 times as fast as in a normally corrosive environment at sea-level pressures - and that is why people who work with oxygen should be as conscious of water contamination and low bottle pressures as they are about flammability of oil and grease contamination.
The question now is: "How many more oxygen bottles are going to be cooking off inflight before CASA/ATSB and QANTAS 'fesses up" to the OTHER complication of their little gaseously malfeasant Nitrogen escapade? An explosion that causes both an explosive decompression at high altitude AS WELL AS compromising the then critical emergency oxygen system is a matter for considerable concern. 365 very lucky people?
Cylinder information
All passenger oxygen cylinders installed in VH-OJK were of a single piece, heat-treated alloy steel construction. The missing (presumed failed) oxygen cylinder, part number 801307-0012, serial number 535657, was one of a batch of 94 cylinders manufactured in February 1996 to the DOT13 3HT1850 specification. The cylinders measured 22.8 cm outside diameter by 75.1 cm long (8.98 inches x 29.56 inches) and had a minimum 2.87 mm (0.113 inch) wall thickness.
Merged: Oxygen tanks topped up with Nitrogen
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Probe after Qantas pumps wrong gas into jets
Matthew Benns
December 16, 2007
POTENTIALLY fatal gas being pumped into passenger jet emergency oxygen tanks in Australia has sparked a worldwide safety investigation.
The Australian Safety Transport Bureau confirmed yesterday that Qantas engineers accidentally put nitrogen into the emergency oxygen tanks of a Boeing 747 passenger jet at Melbourne Airport.
The Australian carrier immediately checked the oxygen supplies of more than 50 of its planes that had been serviced by the mislabelled nitrogen cart at the airport. But an aviation source said: "This could have affected hundreds of planes worldwide. Any international jet that passed through Melbourne and was serviced by Qantas could have had nitrogen pumped into its oxygen tanks."
Health experts warned that in an emergency the effects of nitrogen in the oxygen tanks could have potentially fatal results.
Dr Ian Millar, hyperbaric medicine unit director at The Alfred hospital, said: "If there was an emergency and the pilot took nitrogen instead of oxygen, instead of gaining control of the aircraft he would black out and it would be all over. It's a pretty serious mistake."
Nitrogen, which is non-flammable, is commonly used at airports to fill aircraft tyres. The aviation source said: "Qantas took delivery of the new nitrogen cart 10 months ago. It looked exactly like the old oxygen cart. When the attachments did not fit they went and took them off the old oxygen cart and started using it."
The mistake was eventually spotted by an aircraft engineer. "He was walking around the plane and asked what they were doing. When they said they were topping up the oxygen, he said, 'No you're not, that's a nitrogen cart'," said the source.
The incident was reported to the Civil Aviation Safety Bureau, which confirmed that an investigation detected nitrogen in the crew oxygen tanks on the Boeing 747-300. A bureau spokeswoman said it was a one-off incident.
But the aviation source said: "This has affected at least 175 planes and Qantas has had to tell any other airline that has been serviced in Melbourne to check out its oxygen supplies."
Air New Zealand was told about the problem six weeks ago. "As a result of receiving that letter we did take some precautionary measures," a spokeswoman said. "The oxygen tanks on a small number of planes were removed, checked, reserviced and refilled. No irregularities were found."
A spokeswoman for the Australian Transport Safety Bureau said: "Very clearly they (Qantas) needed to carry out a risk assessment because there was a chance that other aircraft were affected.
"They identified 21 that were at risk because they had had a reasonable amount of oxygen top-up, so there was a reasonable chance they had been contaminated. There were another 30 aircraft at minor risk because they have had minor top ups," said the spokeswoman. The planes were inspected and no positive results found.
She said the airline had turned the error into a learning exercise and informed engineers all over the world about the mistake. "They have talked to thousands of their engineers around Australia and overseas, informing them about this lesson that has been learnt," she said.
Qantas engineering executive general manager David Cox said: "We had a guy using a new rig and he inadvertently serviced the crew oxygen with nitrogen. He realised what he was doing and flagged it."
Mr Cox said that once the mistake had been realised, extensive safety checks were put in place to ensure no other aircraft had been contaminated and that it could never happen again.
"Every aircraft, including customer aircraft, that could have been touched with this rig has been checked," he said after confirming the rig had been in use at the airport for several months. Mr Cox said the airline had been completely open in informing all safety authorities, staff and other airlines about the mistake.
This story was found at:
http://www.theage.com.au/articles/20...568332267.html
NITROGEN USED TO FILL AIRCRAFT OXYGEN SYSTEMS
Airlines all over the world are being warned to check to make sure there’s actually oxygen in their aircraft oxygen systems after an embarrassing mix-up by Qantas Airlines at Melbourne International Airport. For ten months, crews have been filling airliner oxygen systems from a nitrogen cart that’s supposed to be used to fill tires. The mistake went unnoticed until a couple of weeks ago when an observant aircraft engineer spotted service workers using the cart. "He was walking around the plane and asked what they were doing. When they said they were topping up the oxygen, he said, 'No you're not, that's a nitrogen cart,'" an unnamed source told The Age. As anyone who works with industrial gases knows, oxygen tanks have different fittings than other gases to prevent exactly this kind of mix-up. However, when the crews discovered the fittings on what they thought was their new oxygen cart didn’t fit, they swapped them for the ones on the old cart they were retiring. Of course, Australian officials are looking into the error and Qantas has been busy notifying other airlines that use its services in Melbourne. Hundreds of aircraft may be affected.