Check this great post on Amelia Kelly’s blog, Tray Table. She does a great explanation of the “supplementary loop belt” in her post “Babies on the Plane”. This is the lap belt which fixes onto the adults seat belt, it is for infants to age 2 without their own seat, on planes in Australia.
Amelia is an Australian flight attendant for an international airline and wrote this great post in January 2010. If you’ve never flown with a baby before or are uncertain of the regulations relating to restraints for children on board Australian aircraft, this post is certainly worth a look.