((a)) Any justice or judge of the United States appointed to hold office during good behavior who becomes permanently disabled from performing his duties may retire from regular active service, and the President shall, by and with the advice and consent of the Senate, appoint a successor.

((b)) Whenever any judge of the United States appointed to hold office during good behavior who is eligible to retire under this section does not do so and a certificate of his disability signed by a majority of the members of the Judicial Council of his circuit in the case of a circuit or district judge, or by the Chief Justice of the United States in the case of the Chief Judge of the Court of International Trade, or by the chief judge of his court in the case of a judge of the Court of International Trade, is presented to the President and the President finds that such judge is unable to discharge efficiently all the duties of his office by reason of permanent mental or physical disability and that the appointment of an additional judge is necessary for the efficient dispatch of business, the President may make such appointment by and with the advice and consent of the Senate. Whenever any such additional judge is appointed, the vacancy subsequently caused by the death, resignation, or retirement of the disabled judge shall not be filled. Any judge whose disability causes the appointment of an additional judge shall, for purpose of precedence, service as chief judge, or temporary performance of the duties of that office, be treated as junior in commission to the other judges of the circuit, district, or court.