A certificated mechanic may not exercise the privileges of his certificate and rating unless, within the preceding 24 months -
(a) The Administrator has found that he is able to do that work; or
(b) He has, for at least 6 months -
(1) Served as a mechanic under his certificate and rating;
(2) Technically supervised other mechanics;
(3) Supervised, in an executive capacity, the maintenance or alteration of aircraft; or
(4) Been engaged in any combination of paragraph (b) (1), (2), or (3) of this section.