§ 61.183 Eligibility requirements.
To be eligible for a flight instructor certificate or rating a person must:
(a) Be at least 18 years of age;
(B) Be able to read, speak, write, and understand the English language. If the applicant is unable to meet one of these requirements due to medical reasons, then the Administrator may place such operating limitations on that applicant's flight instructor certificate as are necessary;
© Hold either a commercial pilot certificate or airline transport pilot certificate with:
(1) An aircraft category and class rating that is appropriate to the flight instructor rating sought; and
( 2) An instrument rating, or privileges on that person's pilot certificate that are appropriate to the flight instructor rating sought, if applying for—
(i) A flight instructor certificate with an airplane category and single-engine class rating;
(ii) A flight instructor certificate with an airplane category and multiengine class rating;
(iii) A flight instructor certificate with a powered-lift rating; or
(iv) A flight instructor certificate with an instrument rating.
All of this can be found here
[ 16. May 2005, 22:37: Message edited by: c17wannabe ]