Air safety investigators have blamed an exploding oxygen cylinder for blowing holes in the fuselage and floor of a Qantas plane mid-air, and warn it could happen again.
Investigators found the cylinder - one of several in the cargo hold - blew a hole near the wing and shot up through the cabin floor, knocking the plane's door close to the open position.
It came through the floor where a jump seat for crew was located but no one was in it at the time.
The cylinder also hit overhead panelling in the cabin before it dropped back into the hold and was sucked out of the aircraft through the ruptured fuselage.
Debris from the fuselage was also sucked into the No 3 engine, but did not cause major damage.
The Australian Transport Safety Bureau (ATSB) released its preliminary report on Friday, but investigators are yet to determine what caused the cylinder to fail as the plane flew from Hong Kong to Melbourne on July 25, with 346 passengers and 19 crew on board.
While the event was rare, ATSB investigator Julian Walsh said he could not rule out a similar event in the future.
The Boeing 747-400 was 55 minutes into its journey when the explosion occurred at 29,000 feet, causing wind and objects to swirl around the cabin and panicking passengers.
Oxygen masks were dropped and the pilots made a rapid descent to 10,000 feet, before making an emergency landing at Manila airport.
"The passengers were obviously very lucky," Mr Walsh told reporters.
"(The cylinder's) been propelled up with significant force to do the damage that it has, and it's happened very quickly so it probably would have been a matter of seconds."
Mr Walsh said it would be difficult to learn what happened to the cylinder - which had been inspected six weeks before the incident - because it was not available to examine.
"There's nothing at this stage that the ATSB can identify that could have been done to prevent this, we don't really know why the bottle failed - that's the key question for the investigation."
He said he was not aware of a similar occurrence in aviation history but could not rule out such an event happening again.
"Anything's possible, it's certainly a rare event but no one can discount the possibility of those sort of things happening."
The bureau has issued safety advisories to airlines to undertake inspections, testing, maintenance and any required repairs of oxygen bottles.
The team plans to look into the design and manufacture of the cylinders, any recorded failures and the adequacy of inspections and maintenance.
Qantas chief executive Geoff Dixon said the airline's own investigations agreed with the ATSB's preliminary conclusions.
Qantas had completed an inspection of the oxygen systems across its B747-400 fleet on August 1, which confirmed there were no safety issues, Mr Dixon said.
The aircraft involved in last month's incident was repairable at a cost of less than $10 million and would be back in service in November 2008, he said.