Singapore Airlines on Wednesday joined Qantas in grounding some A380 superjumbos to replace their engines after finding oil stains on them.

Australian rival Qantas grounded its six A380s on Thursday, when a Rolls-Royce engine partly disintegrated mid-flight, forcing the fully laden Airbus to make an emergency landing in the biggest incident to date for the world's largest passenger jet.   

Investigations into that incident have focused on oil leaks inside the Rolls-Royce Trent 900 engines, the same model used to power Singapore Airlines' and German Lufthansa's A380 fleet.

But Singapore Airlines stressed the problems on three of its 11 A380s were precautionary and unrelated as the oil stains were different from the oil leakage in the Qantas turbines.

Singapore's findings may deal a fresh blow to Rolls-Royce, which moved on Monday to contain a crisis of confidence, saying it was making progress in understanding what caused last week's blowout on the Qantas A380 flight.

"This is a precautionary move to find out what caused the oil stains," a Singapore Airlines spokeswoman said. "Rolls-Royce recommended a detailed inspection of the engines."    

Singapore Airlines said later its other Airbus A380 aircraft were still in service, but could not rule out further engine changes.

"At this stage there is no indication that more engines on our A380 aircraft will need to have precautionary engine changes carried out, but I would certainly not rule it out," airline spokeswoman Bryony Duncan-Smith told an Australian radio.

Rolls-Royce shares already lost over 7 percent since the Qantas incident, while Airbus and Qantas shares both slipped 2.5 percent each. Singapore Airlines shares were little affected on Tuesday with the stock down 0.4 percent by 0700 GMT.

A spokesman for Rolls-Royce declined to comment.

Experts said the Qantas investigation is pointing to a design fault with the engine which may not be difficult to fix but will take time.

"From information provided to date, it would appear to be a design issue and not a power setting issue. Lower power settings are not the solution," said Peter Marosszeky, an aviation expert at the University of New South Wales.

He added similar engine issues are not unknown to the aviation industry and a fix could be relatively easy, but it could take some time.   

"Until then, what could happen is Airbus would allow operators to fly the A380 on a limited basis with restrictions on the engines," Marosszeky added.   

However, restriction could be a problem for Qantas, as its routes from Los Angeles to Australia are the longest served by the A380, and lower power limits would mean weight restrictions, making flights less economical. - Reuters