Air safety investigators confirmed Friday that an exploding oxygen cylinder ripped a gaping hole in a Qantas jet's fuselage midflight last month, but said they were no closer to solving the mystery of why the tank failed.
Julian Walsh, acting executive director of the Australian Transport Safety Bureau, released an interim report Friday on an ongoing investigation of the emergency aboard a Boeing 747-438 aircraft, carrying 365 people, over the South China Sea on July 25 almost an hour after takeoff from Hong Kong.
The crew quickly descended to an altitude of 10,000 feet (3,000 meters), where oxygen masks were no longer needed, and safely landed at the Philippine capital's airport despite the loss of crucial flight instruments. No one was injured.
The jet remains in Manila, where a physical examination for clues to the cause of the near-disaster has been completed.
Friday's report confirmed early findings that one of seven emergency oxygen cylinders below the cabin floor had exploded, causing the emergency. Walsh said the investigation is now focused on pinpointing the cause.
He said the investigation will likely continue for months and declined to say whether finding the cause was possible.
"There's nothing at this stage that the ATSB can identify that could have been done to prevent this because we don't really know why the bottle failed — and that's the key question for the investigation," Walsh told reporters.
"We haven't got a bottle to work on. Let's not underestimate how difficult it will be for us to get to the bottom of this," he added.
The 26-pound (12-kilogram) steel cylinder, pressurized to 1,850 pounds per square inch (12,755 kilopascals), "sustained a failure that allowed a sudden and complete release of the pressurized contents," Walsh said.
The explosion blew a hole in the fuselage 6.5 feet (202 centimeters) wide and 5 feet (152 centimeters) high, the report said.
Most of the cylinder rocketed up through the cabin floor, shearing off an emergency exit door handle and narrowly missing a crew seat before striking the cabin roof. It ricocheted down through the hole it created in the cabin floor, the report said.
All of the cylinder's remains dropped through the ruptured fuselage and disappeared into the sea.
Walsh said the cylinder had undergone its regulation three-yearly safety inspection shortly before it was installed in the jet six weeks before it exploded.
The report said investigators intend to track down from its U.S. manufacturer other cylinders from the same batch released in 1991 for testing.
Since the emergency, Qantas had completed its fleet-wide inspection of oxygen cylinders without identifying any problems, he said.
Qantas released a statement, backing the preliminary report's findings that an exploding bottle had caused the emergency.
The jet will be repaired for less than 10 million Australian dollars (US$8.6 million) and will be back in service by November, the statement said.
The explosion aboard the flight from London to Melbourne, Australia, has raised questions about the much-lauded safety of Australia's flagship airline, which has never lost a jet aircraft because of an accident.
In the weeks after the incident, Qantas planes experienced a number of other problems, including a loss of hydraulic fuel that led to an emergency landing, failure of landing gear, and detached panels.
The problems prompted the Civil Aviation Safety Authority, Australia's aviation agency, to launch a review of Qantas Airways' safety standards.
Qantas earlier this month temporarily pulled six planes from service because of irregularities in maintenance records. Qantas said it was a record-keeping issue and there were no safety implications for the aircraft.
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