((a)) The chief judge of a circuit may designate and assign one or more district judges within the circuit to sit upon the court of appeals or a division thereof whenever the business of that court so requires. Such designations or assignments shall be in conformity with the rules or orders of the court of appeals of the circuit.
((b)) The chief judge of a circuit may, in the public interest, designate and assign temporarily any district judge of the circuit to hold a district court in any district within the circuit.
((c)) The chief judge of the United States Court of Appeals for the District of Columbia Circuit may, upon presentation of a certificate of necessity by the chief judge of the Superior Court of the District of Columbia pursuant to section 11–908(c) of the District of Columbia Code, designate and assign temporarily any district judge of the circuit to serve as a judge of such Superior Court, if such assignment (1) is approved by the Attorney General of the United States following a determination by him to the effect that such assignment is necessary to meet the ends of justice, and (2) is approved by the chief judge of the United States District Court for the District of Columbia.
((d)) The Chief Justice of the United States may designate and assign temporarily a district judge of one circuit for service in another circuit, either in a district court or court of appeals, upon presentation of a certificate of necessity by the chief judge or circuit justice of the circuit wherein the need arises.
((e)) The Chief Justice of the United States may designate and assign temporarily any district judge to serve as a judge of the Court of International Trade upon presentation to him of a certificate of necessity by the chief judge of the court.