Apparently a hydraulic leak onto the engine which caused the smoke....so not even an engine problem
Quote from channel 10 news, "Plane on fire over Sydney CBD", "Mid-air Mayday"
Funny thing is that they're the worst when it comes to aviation related matters. Remember the United Airlines 747 that had to make a landing in NZ due to a cabin fire.
As they showed the thing land the reporter said "smoke could be seen coming from the wheels as it landed, noone was injured"
The media guys really do know how to scare the public don't they?