Investigators believe an exploded oxygen tank caused the fuselage rupture in the Qantas jet which was forced to make an emergency landing last week.
The investigation, being led by the Australian Transport Safety Bureau, has confirmed that there was one unaccounted for oxygen cylinder.
The tank is designed to provide oxygen to passengers during an emergency. But a number of passengers reported that some of the oxygen masks appeared not to function correctly when they deployed from the overhead modules. This would support the burst tank theory.
Also recovered were a number of component parts including part of a valve in the vicinity of the breech. However, it is yet to be determined whether these components are part of the aircraft system.
Neville Blyth, a senior investigator from the ATSB, said a valve and other small fragments would be tested to determine whether they had come from the oxygen tank.
The fragments were found in the passenger cabin, above where the missing tank, along with five other cylinders, was stored in the cargo hold.
“We recovered ... a valve from an oxygen cylinder,” Blyth told a news conference. “It is likely that that valve is from the missing cylinder.”
If the valve and other fragments are shown to have come from the cylinder, further investigation would be required to determine why the tank burst, he added.
He also added that he did not know of any previous cases in which an oxygen tank had caused an airline accident.
Qantas has ordered all oxygen tanks on its fleet of 747-400s to be urgently inspected.
It has also emerged that the US Federal Aviation Administration issued a directive, which became effective in May, warning airlines to inspect oxygen cylinders on 747-400s.
The directive was issued amid fears they may not have been properly heat treated, which could lead to oxygen leaks and fire hazards. However, David Cox, the Qantas head of engineering, said the FAA directive applied to a different type of oxygen system to the one being scrutinised in the investigation into Friday’s crash.
The plane was carrying 365 people when it was forced to make an emergency landing in Manila after part of the fuselage was ripped open at 30,000 feet, sucking pressure from the cabin.
The Boeing 747-400 had left Hong Kong an hour earlier en route from London to Melbourne when the piece broke off, leaving a gaping four-metre hole down the right side. Passengers reported hearing a loud bang followed by air and debris rushing through the cabin. The pilot made a rapid descent, landing safely in Manila airport.