An engine oil leak caused the explosion on a Qantas A380 super-jumbo that forced it into an emergency landing in Singapore, safety investigators in Australia have concluded.The Australian Transport Safety Bureau (ATSB) said oil leaked into a hot part of the engine and started a fire that eventually caused a turbine disc to fly apart. Sections of a fractured turbine disc and other engine components penetrated the left wing and other parts of the aircraft, resulting in "significant structural and systems damage".Martin Dolan, the chief commissioner of the ATSB, 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."But we think it is significant enough as a safety issue in any event that it needed to be identified and safely dealt with.""As a result of the investigation, the ATSB has issued a safety recommendation about potential engine problems in some Airbus A380 aircraft," the report added.Given its nature, routine maintenance checks would not have identified the problem, the ATSB added.Rolls-Royce, which makes the Trent 900 engine that powered the Qantas airbus, has been threatened with legal action by the airline unless a settlement can be reached over the compensation for lost revenue and additional costs. Qantas grounded all six of its A380s immediately after the incident, but has only resumed flights with two of the planes.