SINGAPORE/SYDNEY (Reuters) - Singapore Airlines will replace engines on three of its Airbus A380 planes after finding oil stains on them, almost a week after Australian rival Qantas grounded its A380 fleet due to an engine failure.

Qantas's six A380s have been grounded since Thursday, when a Rolls-Royce engine partly disintegrated mid-flight, forcing the fully laden Airbus A380 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. Lufthansa said on Wednesday its A380 flights were on schedule.
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.""
Asked if Singapore Airlines was confident the engine maker had identified the cause of the problem, CEO Chew Choon Seng told reporters: ""I'm quite assured at the highest level that Rolls Royce is doing all that it takes to get to that point.""
Singapore Airlines said later its other Airbus A380 aircraft were still in service, but could not rule out further engine changes. It said the engines on the affected aircraft would be swapped in two days.
""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 Australian radio.
-------Investigation focuses on design fault
Rolls-Royce shares have already lost more than 7 percent since the Qantas incident, while Airbus and Qantas shares both slipped 2.5 percent each. Singapore Airlines shares closed 1.2 percent lower on Wednesday.
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.
On Tuesday, a Boeing 787 test flight made an emergency landing in Texas with smoke in the cabin, the first incident of its kind, putting additional scrutiny on the already delayed program.
($1=1.291 Singapore Dollar)
Photo: Technicians inspect a Singapore Airlines' Airbus A380 aircraft at Singapore Changi Airport in this July 4, 2008, file photo.
(Photo: Reuters/Tim Chong