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Sunday, August 31, 2008

Oxygen Bottle Ruptured Qantas 747

Failure of an oxygen bottle caused the fuselage rupture of a Qantas Boeing 747-400 on July 25, say Australian accident investigators, confirming early suspicions.

The event appears to have been unique in commercial aviation history. More importantly, the Australian Transport Safety Bureau (ATSB) has no idea how it can be prevented from happening again—particularly since the bottle fell into the sea and therefore cannot be examined.

“There’s nothing at this stage that the ATSB can identify that could have been done to prevent this,” says investigator Julian Walsh. “We don’t really know why the bottle failed. That’s the key question for the investigation.”

Although the bottle blasted into the cabin, no one was hurt in the incident, which occurred at 29,000 feet. The flight crew reacted within 20 seconds of the depressurization warning by reducing thrust on all engines and extending the speed brakes for a descent to 10,000 feet. They called “mayday” on the regional air traffic control frequency, dumped excess fuel and approached and landed visually at Manila without further incident.

“The flight crew reported that many system failure messages were displayed, including all three instrument landing systems, the left VHF omnidirectional radio-range navigation instrument, the left flight management computer and the aircraft anti-skid braking system,” the bureau says in its preliminary report.

Early accounts seemed to suggest that the main part of the bottle, number four in a row of seven in the cargo bay just ahead of the right wing root, had blasted down and out of the fuselage while the valve at the top had shot up into the cabin.

The bureau’s preliminary report now makes clear that discharge from the lower part of the bottle blew open the fuselage and propelled the main part of the bottle upward. The bottle burst through the main deck, making a hole 20 centimeters (8 in.) in diameter, then hit a door frame, a door handle and the overhead paneling before falling back out of the aircraft, leaving parts of the valve behind.

The implication is that, by a stroke of bad luck, the bottle had managed to escape through the two holes it had already made and then dropped into the sea—and is therefore unavailable for inspection.

The first officer’s aileron cables were severed in the incident, but the captain’s cables on the other side of the aircraft (the left side) were not. “Numerous electrical cables and cable bundles, routed through the lower aircraft fuselage near the point of rupture, had sustained damage or been severed by the rupture event,” the bureau added. “Approximately 86 discrete conductors from six separate bundles had been affected.” [Original article here]

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