14 CFR § 135.321
Except as provided in 135.3, this subpart prescribes the requirements applicable to -
(1) A certificate holder under this part which contracts with, or otherwise arranges to use the services of a training center certificated under part 142 to perform training, testing, and checking functions;
(2) Each certificate holder for establishing and maintaining an approved training program for crewmembers, check airmen and instructors, and other operations personnel employed or used by that certificate holder; and
(3) Each certificate holder for the qualification, approval, and use of aircraft simulators and flight training devices in the conduct of the program.