Australian investigators have confirmed that an exploding oxygen cylinder caused the blast which blew a large hole in a Qantas plane last month.
But they admit they are no closer to explaining why the cylinder blew up.
The incident happened on a Boeing 747 that was flying from Hong Kong to Melbourne on 25 July.
The explosion caused a sudden loss of cabin pressure, forcing an emergency descent to a point where oxygen masks were no longer needed.
The pilot diverted the plane to the Philippines, and it landed safely in Manila despite having a 5 foot (1.5m) hole in its fuselage.
None of the 365 passengers and crew were injured.
Key question
The Australian Transport Safety Bureau (ATSB) released an interim report on Friday, as part of an ongoing investigation into the incident.
The report confirmed early findings that one of seven emergency oxygen cylinders had exploded, blowing a hole in the fuselage and sending the bottle up through the passenger cabin floor.
Julian Walsh, acting executive director of the bureau, said the challenge now was to pinpoint the cause of the explosion.
"There's nothing at this stage that the ATSB can identify what 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," Mr Walsh told reporters.
Source: BBC News