Mr Hill, who is from the Central Coast, said he was less than a kilometre from where the plane came down.
"I saw a light aircraft banking sharply and completely turned on its side. [It] went completely over and went into a bush area about 15 metres from the highway," he said.
"I knew something catastrophic was happening because of the way it was banking.
"It basically banked on its side as it sort of swept over that tree line on the other side of the highway and then it sharply rolled onto it's back and then came straight down.
"It was quite frightening to see actually. And there was no explosion, which was amazing, as it hit that tree line and basically disintegrated."
My italics but the eye witness accounts suggests a possible engine failure and possibly not much fuel on board. Light piston twins can have complicated fuel systems. As the PIC was financially well off and that the aircraft would have been meticulously maintained, I would be surprised if it was mechanical failure.