14 CFR §141.81

1. (a)Except as provided in paragraph (b) of this section, each instructor who is assigned to a ground training course must hold a flight or ground instructor certificate, or a commercial pilot certificate with a lighter-than-air rating, with the appropriate rating for that course of training.
2. (b)A person who does not meet the requirements of paragraph (a) of this section may be assigned ground training duties in a ground training course, if:
   1. (1)The chief instructor who is assigned to that ground training course finds the person qualified to give that training; and
   2. (2)The training is given while under the supervision of the chief instructor or the assistant chief instructor who is present at the facility when the training is given.
3. (c)An instructor may not be used in a ground training course until that instructor has been briefed on the objectives and standards of that course by the chief instructor, assistant chief instructor, or check instructor.