In American Smelting & Ref. Co. v. Arizona Air Pol. C. H. Bd., 113 Ariz. 243, 550 P.2d 621 (1976), an appeal from the Arizona Air Pollution Control Hearing Board (pollution board) was dismissed as moot by the Superior Court of Maricopa County. In that case, the pollution board had entered an order which renewed certain restrictions and the plaintiff, a refining company, had appealed. Sua sponte, the pollution board vacated the order which formed the basis for the refining company's complaint in superior court and ordered a hearing for the purpose of modifying a conditional permit previously ordered. The pollution board then filed a motion in the superior court to dismiss the complaint because the order appealed from had been vacated, and the superior court granted that motion on the ground that the issue had become moot. The refining company appealed upon the basis that its previous appeal had divested the pollution board of jurisdiction to further consider the matter. The Supreme Court of Arizona agreed. In making that decision, the court said, "A board, commission or tribunal can use its appropriate modification power to reconsider decisions until the time when an appeal is perfected." Id. at 244, 550 P.2d at 622. It further said, by way of quoting an earlier case: "'Where an appeal had already been perfected from the judgment of the lower court, the Commission's revocation of the certificate it had theretofore issued to Whitfield was a direct and plain invasion of the appellate and revisory powers of this court. The order in question certainly did not aid the appeal; rather, it would tend to nullify it. The jurisdiction of this court when properly invoked must be protected. It cannot be defeated or usurped to the extent that its decision when rendered be nugatory.'" Id. at 244-45, 550 P.2d at 622-23.