The Tax Court of Canada web site today cleared up a small mystery. Since the appointment of the new Chief Justice there has been no public mention of the plans of former Chief Justice Rip. The web site of the Court today clarified that Justice Rip is now supernumerary:
The Honourable Eugene Rossiter, Associate Chief Justice of the Tax Court of Canada since 2008, has been appointed Chief Justice of the Tax Court of Canada. He replaces the Honourable Gerald J. Rip who elected to become a supernumerary judge.
http://cas-ncr-nter03.cas-satj.gc.ca/portal/page/portal/tcc-cci_Eng/Index 
Tax practitioners will be pleased that the community is not losing the wisdom and experience of Justice Rip, particularly in the case of complex appeals.
Comment: While the Judge’s Act does not explicitly state that a supernumerary judge cannot remain as Chief Justice, it seems implicit in section 28 of that statute:
28. (1) If a judge of the Federal Court of Appeal, the Federal Court or the Tax Court of Canada notifies the Minister of Justice of Canada of his or her election to give up regular judicial duties and hold office only as a supernumerary judge, the judge shall hold the office of supernumerary judge of that Court from the time notice is given until he or she reaches the age of retirement, resigns or is removed from or otherwise ceases to hold office, or until the expiry of 10 years from the date of the election, whichever occurs earlier, and shall be paid the salary annexed to that office.
(2) An election may be made under subsection (1) only by a judge
(a) who has continued in judicial office for at least 15 years and whose combined age and number of years in judicial office is not less than 80; or
(b) who has attained the age of 70 years and has continued in judicial office for at least 10 years.
(3) A judge who has made the election referred to in subsection (1) shall hold himself or herself available to perform such special judicial duties as may be assigned to the judge
(a) by the Chief Justice of the Federal Court of Appeal, if the judge is a member of the Federal Court of Appeal;
(b) by the Chief Justice of the Federal Court, if the judge is a member of the Federal Court; or
(c) by the Chief Justice or the Associate Chief Justice of the Tax Court of Canada, if the judge is a judge of that Court.
(4) The salary of each supernumerary judge of the Federal Court of Appeal, the Federal Court or the Tax Court of Canada is the salary annexed to the office of a judge of that Court, other than the office of a Chief Justice or Associate Chief Justice. R.S., 1985, c. J-1, s. 28; R.S., 1985, c. 16 (3rd Supp.), s. 3; 2002, c. 8, s. 87; 2006, c. 11, s. 7.