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