The rules governing assignment of senior judges are laid out in 28 U.S.C. § 294. In essence, under normal conditions, the chief judge or judicial council of a circuit may assign a senior judge belonging to that circuit to perform any duty within the circuit that the judge is willing and able to perform. A senior district judge can be assigned to an appellate case, and a circuit judge can be assigned to preside over a trial. For courts that do not fall within a circuit, such as the United States Court of International Trade, the chief judge of that court can assign a senior judge of that court to perform any duty within the circuit that the judge is willing and able to perform.