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SYDNEY--An onboard oxygen bottle has never before exploded on a passenger jet in mid-air, an Australian air safety official said Monday, as investigators probed the cause of a huge hole in a Qantas jumbo.
The Australian carrier is carrying out urgent inspections of oxygen bottles on its entire fleet of Boeing 747s after the fuselage of a 747-400 was ripped open, forcing an emergency landing Friday in Manila.
"As far as we can determine this has never happened before on a passenger aircraft," Civil Aviation Safety Authority (CASA) spokesman Peter Gibson told the Australian Broadcasting Corporation.
"There's no reports of it anywhere, so it's very, very unusual and obviously understanding why that happened will be absolutely critical to making sure it can't occur again," he said.
Australian Air Transport Safety Board (ATSB) investigators are focusing on whether an oxygen bottle used for emergency back-up for the cockpit exploded mid-flight, tearing a three-meter (10 foot) hole in the Boeing's hull.
One of two such cylinders is missing from the plane that made an emergency descent and landing in the Philippines capital Friday with 365 passengers and crew on board, investigators said.
"If it turns out that is the cause of the accident, the cause of the hole in the side of the aircraft, obviously that will be a key part of the investigation working out why a bottle would suddenly give way," Gibson said.
Metal fatigue in the cylinder, a failure of the regulator valve, something hitting it and puncturing the bottle, or it overheating, were among possible causes the ATSB would look at, he said.
"Maintenance has to be looked at obviously, yes you can't rule that out, but at this stage you look at absolutely everything," Gibson told ABC radio.
Qantas said Sunday it had ordered checks on the oxygen bottles -- they are due to be completed this week -- after Australian investigators leading the probe in the Philippines revealed a cylinder was missing from the plane.
