Media reports a witness saying the aircraft was revving out of control and not climbing. Another report that the aircraft had a Subaru engine. Aircraft fitted with Subaru engines that I have seen have had belt driven reduction gearboxes.
If this aircraft had a similar set up, a belt failure would result in symptoms reported by the witness.
https://www.aap.com.au/news/doomed-s...erimental-kit/
https://7news.com.au/news/disaster-a...ball-c-9285544