What are the laws on photographing aircraft in Australia?
There is no law in Australia prohibiting the photography of aircraft. I have been approached by police while doing it just to see what I was up to, but after a polite exchange they were happy and moved on.
Potentially, if you're on private property (eg an airport terminal), the conditions of entry are allowed to prohibit the taking of any photos. But I'd be shocked if that is applied anywhere outside of theatres or defence bases. You try telling travellers they're not allowed to take an airport selfie for instagram.
If you're using the photos for commercial reasons, and they include a trademark (like an airline logo), you might need to contact them for permission, I'm not certain how that process works. But this certainly doesn't apply for private use.
Having said all that, I am not a lawyer, so if you're worried or want specific information you should at least ask on a legal forum, if not pay for a professional opinion.