The investigation of the engine failure that grounded Qantas' fleet of superjumbo jets is making progress, manufacturer Rolls-Royce said, while the Australian airline announced that tests uncovered worrying oil leaks in the engines of three more Airbus 380s.
Australia's national carrier said its fleet of six double-decker planes would stay grounded for another 72 hours.
Airbus and other airlines said they would take no action until the investigation is completed, and that it was premature to contemplate any change from the Rolls-Royce Trent 900 engines mounted on many of the A380s — the world's largest passenger jet.
Meanwhile, a European aviation official said the engine's design features had prevented a worse tragedy from occurring after it blew up.
Rolls-Royce Group PLC stock rose more than 2 percent on the London Stock Exchange after the company issued a brief statement Monday saying the tests were "being progressively completed." It said the problem had been isolated to its Trent 900 family of high-bypass fan engines, but provided no further details on how long the inspections would take. Shares in Rolls-Royce Group were down 8 percent Friday.
An engine on a Qantas Airbus 380 exploded minutes into a flight from Singapore to Sydney on Thursday, scattering debris over Indonesia's Batam island. The plane, carrying 466 people, returned to Singapore and made a safe emergency landing.
The version of Rolls-Royce Trent 900 engine used by Qantas differs slightly from those installed on the A380s of other airlines — Lufthansa and Singapore Airlines — because it is a little more powerful.
The Australian Transport Safety Bureau, which is leading an international investigation of the incident, has appealed for help to find a missing piece of a turbine disc, saying it may be crucial evidence needed to fully understand what caused the engine to burst.
The agency released a photo of a jagged and bent piece of turbine disc from the Trent 900 and asked that anyone finding a similar piece should give it to police.
The photos appeared to indicate a failure of the metal disc at the center of the jet turbine. These spin at speeds of 12,000 rotations per minute at high power settings during takeoff and the initial climb, generating immense centrifugal forces.
The most frequent causes of engines breaking up are the ingestion of objects on the runway or bird strikes at those moments. Mechanical problems such as rotor imbalances or metal fatigue can cause microscopic cracks to form on the rotating elements, leading to their failure.
John Goglia, a former U.S. National Transportation Safety Board member and an expert on aircraft maintenance, said there are several reasons why a disc might fail, and they usually involve the metal used to make the component or the manufacturing method.
On Monday, Qantas CEO Alan Joyce said engineers have discovered oil leaks in the turbine area of three engines on three different A380s.
"The oil leaks were beyond normal tolerances," Joyce said. "All of these engines are new engines on a new aircraft type."
Because of that, he said, all of the airline's A380s will be grounded for at least an additional 72 hours. "We are not going to take any risks whatsoever," Joyce said.
Lufthansa and Singapore Airlines also briefly grounded their planes last week, but resumed service after checking the engines.
Airbus spokesperson Aude Lebas said the airframe maker was not aware that any airlines that had ordered the Trent-equipped A380 were contemplating changing their orders for an alternate engine built by Engine Alliance, a 50-50 joint venture between GE Aircraft Engines and Pratt & Whitney.
David Henderson, of the Association of European Airlines, said it was very unlikely that any of the customers that had ordered a total of 234 superjumbos would consider swapping engines.
"I've never before heard of anyone switching engines once an order has been placed," he said.
Meanwhile, a civil aviation regulator said the investigation showed that the design of the engine, its casing and the aircraft's wing had prevented damage to critical aircraft systems.
The official, who declined to identify himself because he was not authorized to release the information, said that despite the uncontained failure — in which parts of the jet turbine break free and break through the protective casing — the engine had performed exactly as it was designed to do in a worse-case scenario.
Most of the debris was ejected to the sides or downward, and none of the vital components, such as the plane's hydraulics systems or fuel tanks, had been punctured, he said. This allowed the crew to maintain control, circle for a period of time while dumping excess fuel, and — after the landing — for passengers to disembark without resorting to an emergency evacuation.
In one of the best-known incidents of uncontained engine failure, a United Air Lines DC-10 crashed in 1989 while making an emergency landing at Sioux City, Iowa, after the metal hub that holds the engine's fan blades shattered and ruptured the jet's hydraulic control lines. A total of 111 people on board perished in the accident, while 185 survived.
Although the A380 has generally been reliable since its introduction into service three years ago and is popular with both crews and passengers, it has had problems common to new types of airliners.
In September 2009, a Singapore Airlines A380 was forced to turn around and head back to Paris after an engine malfunction. In August, a Lufthansa crew shut down one of the engines as a precaution before landing at Frankfurt on a flight from Japan, after receiving confusing information on a cockpit oil pressure indicator.
Lekic reported from Brussels. Raphael G. Satter contributed to this report from London.