Sydney, Australia:
A report by Australian aviation investigators on Friday provided fresh insight on the challenges faced by a Qantas A380 jet that experienced a mid-air engine explosion last month, describing in vivid detail the damage sustained to the plane's wing and fuel systems and lauding the crew's calm and professionalism in bringing the crippled jet with 469 people aboard to a safe landing in Singapore a mere 150 yards from the end of the runway.
The official interim report issued by the Australian Transport Safety Bureau echoed fresh safety recommendations and airworthiness directives issued Thursday for the Rolls-Royce Trent 900 engines after investigators found a potential manufacturing defect that may have contributed to the leak.
"The aircraft would not have arrived safely in Singapore without the focused and effective action of the flight crew," the bureau's chief commissioner, Martin Dolan, told reporters in Canberra on Friday.
The investigator's report confirmed that metal fragments from the splintered turbine of the plane's No. 2 engine tore holes in the left wing and fuselage minutes after takeoff from Changi International Airport as the plane ascended through 7,000 feet elevation. The explosion triggered a cascade of electrical and hydraulic failures and emergency warnings in at least 10 other areas of the aircraft, leaving the plane with limited flight controls, the report said.
The crew of five pilots reported hearing "two almost coincident 'loud bangs,' followed shortly after by indications of a failure of the No. 2 engine" and intermittent warnings of an engine fire, the report said. After several attempts, the pilots were able to shut down the damaged engine and, despite a cacophony of alarms and warnings flashing on the cockpit computers, were able to maintain control of the plane as they alerted air traffic control in Singapore of their problem.
The extent of the damage only became clear after the plane's co-pilot entered the cabin to visually assess the situation. A passenger, another Qantas pilot, showed him video from a camera mounted on the plane's tail that fed into the plane's in-flight entertainment system -- a feature unique to the A380. That display showed a half-meter wide gush of liquid -- most likely a mix of fuel and hydraulic fluid -- streaming from underneath the left wing.
As the plane lost fuel, its center of gravity began to shift, potentially threatening the plane's stability. But damage to fuel and hydraulic lines made it difficult for the crew to transfer fuel to other tanks.
The report said the crew faced so many alerts that it took nearly an hour to respond to them before they could begin coordinating plans for landing with air traffic controllers. During that time, the plane circled in a holding pattern close to the airport with the autopilot engaged.
In fact, the number of warnings was such that the plane's computers could not initially make an accurate calculation of whether the jet -- still laden with fuel and 50 tons over its maximum landing weight -- would be able to slow itself enough on landing to avoid overshooting the end of the runway.
In the end, the pilots -- who had a combined 72,000 hours of flight experience -- removed some variables from the landing calculations. The computer indicated a safe landing would be possible, but the pilots, nonetheless, instructed flight attendants to prepare for an emergency evacuation if the plane ended up in the water beyond the runway's end.
An hour and a half after the explosion, the plane stopped with just 150 yards of concrete to spare, its brakes heated to 1,650 degrees Fahrenheit, and four of its 22 tires blown.
The safety board said its "very complex investigation" would continue, in close cooperation with safety regulators and accident investigators in Europe and Singapore. The agency said it expected to complete its inquiry by November 2011.
On Thursday, investigators said that uneven boring inside an oil tube within a combustion chamber had caused thinning of the metal on one side of the tube. Investigators believe that the fault may have led to a fatigue crack from which oil could have leaked into the super hot engine, creating the explosion that caused one of the turbine discs to splinter and fly off the engine, damaging the plane's left wing and fuselage.
Twenty-one A380s operated by Qantas, Singapore Airlines and Lufthansa use the Trent 900 engine. Eighteen other A380s, operated by Air France and Emirates, use a different engine.
In response to the safety recommendation, Qantas briefly grounded its two A380s that are currently in service and subjected them to special tests to see whether the misaligned boring was present in the oil tubes. The two jetliners were cleared to return to service on Friday with the approval of Australia's airline safety regulator, the Civil Aviation Safety Authority.
Four Qantas A380s that normally fly the lucrative Sydney to Los Angeles route remain grounded, under the airline's voluntary agreement with Australian regulators not to fly the A380s on any route that requires the engines to operate at full thrust until further notice.
In a brief statement, Rolls-Royce said it would continue to cooperate with international investigators, and would work with aviation regulators, Airbus and its airline customers to "progressively allow the whole fleet of Trent 900 powered Airbus A380s to return to service."
Testing for the misaligned boring, which was discovered at the Rolls-Royce plant in Britain on Wednesday, has required "a very highly specialized inspection procedure and equipment," Mr. Dolan said. "Given that no one was aware that the potential problem existed, it's highly unlikely that any maintenance would have been able to establish that this was a potential problem."
John Page, a senior lecturer in aeronautics at the University of New South Wales, with more than 50 years experience in aviation mechanics, said that fatigue failures were often hard to detect.
"The trouble with fatigue is that when it goes, it goes very suddenly. It wears very gradually and you don't notice it," he said. "You would assume that there may have been a very slight oil sweating beforehand, but you'd never notice that. This is not a clean part of the engine."