ATSB fails to find cause for Qantas cylinder rupture
06 Mar 2009 1:45 PM
CANBERRA, March 6 AAP - How an oxygen cylinder came to blow a hole in a Qantas jumbo jet carrying 365 passengers and crew on a flight out of Hong Kong remains a complete mystery.
The Australian Transport Safety Bureau (ATSB) said the cylinder, which penetrated the cabin and skin of the aircraft, causing a loss of cabin pressure, had never been found, so the exact reason for the malfunction could not be determined.
There was no trace of any explosive residue that would point to a terrorist attack.
The ATSB and aircraft manufacturer Boeing examined a number of cylinders from the same production batch.
"To date, the investigation has not identified any verifiable deficiency in the cylinder design," the ATSB said in an interim safety report released Friday.
"The investigation is continuing."
The ATSB said cylinders had failed on other aircraft, but always as a result of external causes such as fire.
"While the history of cylinder failure remains under examination, the characteristics of the occurrence event appear to remain unique in worldwide experience," it said.
The mishap occurred as the Qantas Boeing 747 jumbo jet flew from Hong Kong to Melbourne on July 25, with 346 passengers and 19 crew on board.
As the aircraft cruised at 29,000 feet some 55 minutes after take-off, a loud bang was heard by passengers and crew, followed by the rapid cabin depressurisation.
The aircraft descended and landed safely at Manila.
No one was hurt, but an inspection revealed a two-metre rupture in the fuselage.
Engineers concluded that one of seven passenger oxygen cylinders had failed.
The discharge of the pressurised oxygen ruptured the fuselage and propelled the 75cm cylinder upwards through the cabin and into the passenger cabin where it hit a door frame, door handle and overhead panelling.
The cylinder, manufactured in 1996, was never found. It had been routinely inspected and tested, most recently just two months earlier.
Other cylinders, the oldest made in 1989, showed no sign of problems.
Just as mysterious as the cylinder's failure is why it was never found.
The ATSB said the cylinder most likely fell from the aircraft, even though the entry hole through the cabin floor was small.
Other possibilities - though unlikely - are that the cylinder remains somewhere aboard the aircraft or that it was souvenired by a passenger.
Qantas chief executive Alan Joyce said investigations to date continued to support the airline's own findings.
He said this, and other incidents involving the failure of a navigation instrument on a Qantas flight from Singapore last year, were rare if not unique events.
"We, and all airlines operating these aircraft types, are keen to fully understand what contributed to these highly unusual incidents," he said in a statement.
"Safety remains our highest priority, and we will continue to work closely with the ATSB, CASA (Civil Aviation Safety Authority) and manufacturers on these ongoing investigations."
AAP mb/kms/jl/mo
