An oil leak was the most likely cause of the mid-air disintegration of a superjumbo engine last month that prompted a global safety review of the world's newest and largest jetliner, investigators said in a preliminary report on Friday.
The Australian investigators also said they found a potentially dangerous manufacturing defect that may still exist in Rolls-Royce engines used by three airlines on their Airbus A380s. Airlines said they were already checking for the new problem.
The Australian Transport Safety Bureau released its first report into the blowout that caused a Qantas A380 to make an emergency landing in Singapore on Nov. 4 in what was the most significant safety issue yet for the giant jumbo since it began passenger flights in 2007.
The bureau confirmed earlier suggestions that oil leaking from tubes in a super-hot part of the engine likely caused a fire that eventually caused a heavy turbine disc to fly apart, sending shrapnel slicing through a wing and scattering debris across Indonesia's Batam island.
The ATSB said it had found a suspected manufacturing flaw in oil tubes in part of the engines and recommended new safety checks for A380s using those engines. Twenty A380s are powered by Trent 900 engines across three airlines: Qantas, Singapore Airlines and Germany's Lufthansa.
The Australian agency, which is leading the international investigation into the Qantas engine breakup, said a section of an oil tube that connects the high-pressure and intermediate-pressure bearing structures of the engine was the danger area.
The problem could lead to "fatigue cracking, oil leakage and potential engine failure from an oil fire," the agency said.
"We are not yet at a stage where we can definitively say that the potential fatigue problem with the oil pipe that has been detected is the cause of what happened over Batam island," ATSB chief commissioner Martin Dolan told reporters. "But we think it is significant enough as a safety issue in any event that it needed to be identified and safely dealt with."
The ATSB said Rolls-Royce, affected airlines and other safety regulators were responding to the findings with action to ensure the A380s involved were safe.
The agency's report also showed the engine blowout led to a series of electrical and computer system failures that forced the pilots to land the plane in difficult conditions. The plane's autopilot function disconnected about 1,000 feet (305 meters) from the runway, leaving the pilots little choice but to fly the aircraft manually for the rest of the approach.
"The aircraft would not have arrived safely in Singapore without the focus and effective action of the flight crew," Dolan said.
The report detailed a series of system shutdowns that occurred during the incident. After the engine failure, the pilots received a flood of electronic warnings about a series of electrical and computer system failures: the wing slats were inoperative and the plane's auto-thrust and auto-land weren't working. There were warning messages about the brakes and landing gear, the engine's anti-ice mechanism, the plane's center of gravity and other systems.
Reverse thrust, which slows the plane down on the runway, was only available from one of the four engines. Another message warned the pilot not to apply maximum braking until the plane's nosewheel was on the runway.
In those conditions, the crew knew there was a possibility they'd overrun the airport's runway. The autopilot disconnected a couple times during the plane's early approach, but a crew member managed to reconnect it. With just 1,000 feet (305 meters) to go, it disconnected again, leaving the pilot little choice but to fly the aircraft manually for the rest of the approach. Still, he landed the aircraft safely, pulling the plane to a complete stop less than 500 feet (150 meters) from the end of the runway.
Planes using Trent 900 engines underwent extensive checks and modifications to comply with a Nov. 11 directive from the European Aviation Safety Agency that warned of dangerous oil leaks following the Qantas incident.
On Thursday, the agency said it had no immediate plans to change that directive following the ATSB's recommendations.
"We believe the safety of the engines is ensured by our previous airworthiness directive, namely the engine inspections," spokesman Dominique Fouda said. "But if there are additional findings in the next several days, we reserve the right to change that directive."
Qantas, which grounded its six A380s for 19 days after the blowout, said Friday it had completed the new checks on one of the two A380s it has returned to service, and had found no problems. The others are still undergoing tests. Singapore Airlines, which has 11 A380s, also said it was conducting new checks of its engines.
Dolan said the European agency had approved plans to upgrade software for the Trent 900 that would shut down an engine if it began to have problems such as those encountered on the stricken Qantas flight.
The ATSB it is still investigating the incident, and it's full report could take a year.
Meanwhile, Qantas said Thursday it filed a statement of claim in an Australian court that will allow it to pursue possible legal action against Rolls-Royce if it isn't satisfied with a compensation offer from the engine manufacturer.
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