Nojwod, quite correct, It doesnt necessarily follow that the initial descent was deliberate. Human Factors play a huge role in this accident, before he even turns around his mindset is, track direct to bankstown and descend to circuit height, initially even if he was at optimum climb configuration, the aircraft is doing exactly as his mindset expects. Situational awareness doesn't come until there's a mismatch, probably at some point before reaching 2.500'ft. Certainly he is fully aware by 1500ft, because we hear disbelief in his voice.
ScotCD
You Sir are an important witness, because you are one of the few that saw the aircraft in it's last seconds of the en-route phase, beyong this point he is landing. We all have lots of questions for you, the ones I would ask have already been asked by Remoak and Griffo