It's limited to errors of law, but including whether or not there was sufficient evidence to support the factual conclusions, for example, being considered an error of law. Basically, it's a determination of whether or not the tribunal was patently unreasonable in reaching a conclusion based on the evidence before it, whether the tribunal strayed beyond its jurisdiction, and the usual types of judicial reviews that quasi-judicial tribunals are subjected to.
It's the Federal Court of Appeal, by the way, not the Federal Court.