The clues about the cause of the ugly Qantas laundry drop at Manila last Friday are falling into place.

On 24 April CASA issued an airworthiness directive with an enforcement date of 5 June requiring urgent inspections of the supports that held oxygen bottles in place on Boeing 747s like the one that was only an hour into a Hong Kong-Melbourne flight with 365 people on board when it made an emergency descent into Manila with a large load of passenger luggage plugging a gaping hole below the cabin and forward of the wing.

This AD as they are called was CASA’s immediate response to disturbing news from the Federal Aviation Authority in the US warning that some of these supports might fail, releasing high pressure oxygen bottles and risking a leak.

The rack that held oxygen bottles on QF 30 is in fragments near the fuselage rupture and two of the scuba-dive-sized bottles are missing.

There is no sign of fire. Or of a massive explosion, since even one of those bottles, if detonated, would most likely have blown the forward section of the jet apart from the main body, just like the bomb on a Pan Am flight which detonated in the same area of the cargo hold over Lockerbie in Scotland on 21 December 1988.

But experts say the release of a stream of high pressure oxygen on its own could ram a bottle through the fuselage of any jet, whether brand new or riddled with rust.

The question remains unanswered as to whether the fuselage blew first, because of an undetected imperfection, or over repair as some engineers have speculated, causing the luggage container to get sucked backwards to the hole and slamming into the oxygen bottle rack in the process, or the bottles initiated the failure by falling out of their supports and ‘going off’.

This morning’s new directive from CASA, for all oxygen bottles in the 747s to be checked, is a solid belt-and-braces follow up.

Now the outstanding queries about QF 30 include whether the original AD was complied with. There have been reports that during the 10-week engineering overtime bans, the papers carried by this jet noted that the oxygen system needed to be checked on a per flight basis.

Even before the maintenance dispute, the jet was flying, again like much of the Qantas fleet, with a long list of time-limited permissible defects.

When Captain John Bartels began the diversion he lost an unspecified range of instrumentals and controls. Qantas has again been lucky to have such a serious incident happen so close to an airport.

Had this occurred say mid way to Johannesburg, or somewhere between Los Angeles and Australia, the jet, forced to fly at less than 10,000 feet would have consumed much more fuel than normal, and it could have all ended rather badly.

The same luck was there when QF 2 lost most of its electrical systems just short of Bangkok on 7 January. That jet had only minutes of battery power remaining. On New Year’s Eve it was on a sightseeing charter over Antarctica, from where it would not have safely returned.