28 U.S.C. § 294 : US Code - Section 294: Assignment of retired Justices or judges to active duty

Search 28 U.S.C. § 294 : US Code - Section 294: Assignment of retired Justices or judges to active duty

(a) Any retired Chief Justice of the United States or Associate
Justice of the Supreme Court may be designated and assigned by the
Chief Justice of the United States to perform such judicial duties
in any circuit, including those of a circuit justice, as he is
willing to undertake.
(b) Any judge of the United States who has retired from regular
active service under section 371(b) or 372(a) of this title shall
be known and designated as a senior judge and may continue to
perform such judicial duties as he is willing and able to
undertake, when designated and assigned as provided in subsections
(c) and (d).
(c) Any retired circuit or district judge may be designated and
assigned by the chief judge or judicial council of his circuit to
perform such judicial duties within the circuit as he is willing
and able to undertake. Any other retired judge of the United States
may be designated and assigned by the chief judge of his court to
perform such judicial duties in such court as he is willing and
able to undertake.
(d) The Chief Justice of the United States shall maintain a
roster of retired judges of the United States who are willing and
able to undertake special judicial duties from time to time outside
their own circuit, in the case of a retired circuit or district
judge, or in a court other than their own, in the case of other
retired judges, which roster shall be known as the roster of senior
judges. Any such retired judge of the United States may be
designated and assigned by the Chief Justice to perform such
judicial duties as he is willing and able to undertake in a court
outside his own circuit, in the case of a retired circuit or
district judge, or in a court other than his own, in the case of
any other retired judge of the United States. Such designation and
assignment to a court of appeals or district court shall be made
upon the presentation of a certificate of necessity by the chief
judge or circuit justice of the circuit wherein the need arises and
to any other court of the United States upon the presentation of a
certificate of necessity by the chief judge of such court. No such
designation or assignment shall be made to the Supreme Court.
(e) No retired justice or judge shall perform judicial duties
except when designated and assigned.