From memory, as long as they appeal within 5 working days to the AAT then they can continue to operate for at least another 90 days. After that if the case has still not come before the AAT then they will be granted an extension until it does. It is feasible that the issue may not be resolved for another 6 months. CASA do have the authority to pull an AOC if they consider the operator to be a threat to public safety blah blah blah - but in my opinion if they are taking the AAT route then they probably don't have much of a case and it will probably end up as an Enforceable Voluntary Undertaking (EVU) - again CASA talk for we've got nothing but have to look like we are doing something.