The Federal Aviation Administration (FAA) defines
who may perform maintenance on certificated
aircraft in FAR 43.3. This rule lists all the usual
certificated suspects: mechanics, repair stations,
air carriers, repairmen employed by a repair station
or air carrier, and (under certain conditions) aircraft,
engine, propeller and appliance manufacturers. The
rule also permits maintenance to be done by ordinary
noncertificated folks, provided it’s done under the
supervision of and approved by a certificated mechanic.