CANBERRA, Australia – An oxygen bottle explosion that tore a hole in a Qantas jumbo during a flight two years ago was a unique event that is extremely unlikely ever to happen again, investigators said Monday in their final report into the incident.
But the investigators concluded the exact cause of the incident would never be known because the key piece of evidence — the oxygen tank — fell into the South China Sea and was never recovered.
The Australian Transport Safety Bureau report into the July 2008 incident is unrelated to the blowout of a Rolls-Royce engine on a Qantas superjumbo earlier this month, but both events are part of a string of safety incidents in recent years that have tested the Australian airline's reputation as one of the world's safest.
The latest incident also involves parts not likely to be recovered, with some of the Airbus A380's engine parts still lost after the blowout over an Indonesian island. However, safety bureau chief commissioner Martin Dolan said he did not expect a similarly inconclusive result for the superjumbo investigation. A preliminary report on that investigation is due next week.
"We've got most of the necessary engine when it comes to the 380 and we've got significant components that have given us enough information already to establish reasonably clearly what's going on there and that will be reflected in our interim report," Dolan told reporters.
On the Boeing 747 oxygen bottle explosion, investigators had been unable to replicate that rupture in experiments with similar U.S.-manufactured steel tanks.
"Given the widespread and long-term use of this type of cylinder, it was clear that this occurrence was a unique event," Dolan said. "It is our view that the risk of a similar rupture and consequent aircraft damage remains extremely remote."
Investigators speculated that the tank's flaw lay in the manufacture of the steel with which it was made, and that that fault could have been impossible to detect, Dolan said.
Qantas welcomed the report's finding that the emergency was unique and without precedent.
"Importantly, the report makes no findings in relation to Qantas' engineering and maintenance operations," the airline said in a statement.
The Boeing 747 was flying across the South China Sea carrying 369 passengers and crew from London to Melbourne, Australia, when the oxygen bottle — one of a bank of seven stowed in a cargo hold to supply passengers' oxygen masks in an emergency — split in two.
The lower part blew a gaping hole 79 inches by 60 inches (2 meters by 1.5 meters) in its fuselage, while the top shot through the passenger cabin floor and sheared off an emergency door handle before it bounced off the ceiling and ricocheted back through the floor. The explosion caused rapid cabin decompression and damaged navigational instruments.
No one was injured and the jet landed safely in the Philippines, but questions were raised about the much-lauded safety record of Qantas, which has never lost a jet airliner in an accident.
It was among a series of high profile incidents that prompted Australian air safety regulators to order Qantas in September 2008 to improve its maintenance system.
The Civil Aviation Safety Authority said it found deficiencies and "signs of emerging problems" in the way Qantas manages and delivers maintenance to its planes.
Questions over Qantas safety flared anew when one of the airline's Airbus A380 superjumbos was damaged by an engine explosion over Indonesia on Nov. 4. Qantas' fleet of six A380s remain grounded while the airline swaps out some parts of the Rolls-Royce Trent 900 engine they use and conducts safety tests. Other airlines using the A380 with Trent 900 engines are still flying the planes.
In its report Monday, the transport bureau said the cylinder design was "inherently robust" and there was no evidence suggesting Qantas' handling, operating or maintenance procedures had contributed to the failure. It said it has found no record of any other related instances of aviation oxygen cylinder rupture.
The jet involved has returned to service, but has continued to attract unwelcome attention for Qantas. After it was repaired in Manila, it collided with another 747 on a Melbourne airport tarmac in November 2008 while airline staff were towing it. There were no passengers aboard either jet and no one was injured.
The same jet was diverted during a flight from Singapore to Sydney in September 2009 when cockpit instruments registered a fuel leak. The jet landed safely with 290 passengers aboard in the western Australian city of Perth.