On 1st July 2015 the Migration Review Tribunal, Refugee Review Tribunal and Social Security Appeals Tribunal were merged with the AAT. Therefore MRT, RRT are now AAT.
The AAT can only review a decision if an Act, Regulation or other Legislative Instruments states that state that the decision can be reviewed by the AAT
The AAT reviews a decision "on the merits". This means that AAT will take a fresh look at the facts, law and policy relating to the decision and arrive at their own decision. The AAT must make the legally correct decision or, where there can be more than one correct decision, the preferable decision.