I don't disagree with a police to search a aircraft, with the proviso that there is reasonable cause. I would expect their warrant card entitles them to detain and search in any case.
The reality is that if and when we have a (real) aviation terrorist incident in Oz, the investigation will no doubt reveal that the perp DID NOT have an ASIC and the aircraft was NOT searched by police.
To a terrorist, aircraft other than RPT would probably be of little interest, so maybe they'll copy what they did in Iraq where they regularly kill scores of people with cars, trucks, bicycles and explosive garments.
I imagine they could fill up a cement mixer with explosive and nuts and bolts and detonate it at a place of their choosing. After that, the "authorities" will then insist on a CMDSIC (Cement Mixer Driver Security Identity Card).
Or maybe anyone with a backpack (remember London 2005?) will need to pay $186 for a police background check before they get their BPSIC, and of course, renew it every 2 years.
Terrorists will always be a step ahead of authorities and have shown they will be creative and resourceful in their endeavours, i.e we would never have known of the "Shoe Bomber" had his plan been successful. They will play the odds and keep coming up with something new.
I should mention the security guards on the Harbour Bridge. IMHO they will simply be additional victims, but then it will break their boredom. Their chances of stopping something is zero.