US aviation authorities warned of problems with oxygen tanks on board Boeing 747s months before the explosion that ripped a hole in a Qantas jumbo jet on Friday, it has emerged.

The US Federal Aviation Administration had ordered thorough checks of US-registered Boeing 747s after a report found many of the oxygen cylinders needed to be replaced.

“We are issuing this [directive] to prevent failure to oxygen cylinder support under the most critical flight load conditions, which would cause the oxygen cylinder to come loose and leak oxygen,” the FAA told airlines.

A faulty oxygen cylinder is thought to be at the centre of the explosion on board a Qantas jet on Friday which ripped a 10ft hole in QF30, which was en route from London to Melbourne via Hong Kong.

The explosion forced the 747, with 346 passengers and 19 crew on board, to descend 20,000ft and make an emergency landing in Manila.

Investigations continue in Manila today, however officials said an oxygen back-up cylinder was missing from the aircraft, and have ordered Qantas to inspect all such bottles on its fleet of Boeing 747s.

Qantas began to inspect their 30-strong 747 fleet this morning.

An investigator from the Australian Transport Safety Bureau, Neville Blyth, said: “It is too early to say whether this was the cause of the explosion, but one of the cylinders which provides back-up oxygen is missing.” He said investigators had ruled out terrorism.

Geoff Dixon, Qantas CEO, said that whatever caused a mid-air emergency was more than likely beyond the control of the airline.

He told a news conference today that the cause of the incident that ripped the giant hole in the fuselage of the passenger jet was a mechanical fault.

Mr Dixon also said that the US warning in April about oxygen tank concerns on airliners was not anything to do with the potential cause of Friday's incident.

A spokesman for Australia’s Civil Aviation Safety Authority (CASA), Peter Gibson, said that the American directive was limited to a certain number of support brackets, racks that held the oxygen tanks in place on the plane, and not the actual bottles.

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