From the CASA website...
Civil Aviation Safety Authority - Your ASIC questions answered
Q: What are the security requirements?
You need a valid ASIC if you require frequent access to a secure area of a security controlled airport that has Regular Public Transport (RPT) operations. This is a requirement of the Aviation Security Regulations 2005.
If you want to use your CASA issued flight crew licence and you do not require frequent access to a secure area of a security controlled airport that has RPT operations, you must apply for a background security check and you will be issued with an AVID provided your checks are successful. This does not apply if you are under 18.
Q: Are pilots still allowed to fly without an ASIC?
Yes. Pilots only need to have submitted an application for an AVID or an ASIC to operate an aircraft. The application will be processed and appropriate background checks undertaken prior to the AVID or ASIC being issued to an eligible pilot.
Kaz