So what happened?
I think we can agree now no fan blades left the engine and it was a failure of the cowling. Was this perhaps a panel not properly tightened?
A 'big bang' was heard by multiple different people on the ground over a Sydney suburb. (It's widely reported on social media), so we can assume the cowling went into the engine causeing failure?
Me thinks this is a mantaince screw up. It would be interesting to see who last had hands on the cowling.