The holder of a ground instructor certificate may not perform the duties of a ground instructor unless, within the preceding 12 months:

(a) The person has served for at least 3 months as a ground instructor; or

(b) The person has received an endorsement from an authorized ground or flight instructor certifying that the person has demonstrated safisfactory proficiency in the subject areas prescribed in §61.213 (a)(3) and (a)(4), as applicable.