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.