Regulations, Publications, and Airman Certification Requirements
What a ground instructor certificate actually permits
The ground instructor certificate lives in 14 CFR Part 61, subpart I. Eligibility is narrow and often misremembered: you must be at least 18, read/speak/write English, pass the Fundamentals of Instructing knowledge test, and pass the knowledge test for the rating sought (Advanced Ground Instructor). No medical certificate and no pilot certificate are required. Ratings: Basic (private and recreational), Advanced (adds commercial and instrument ground training), Instrument (instrument only). AGI is the broadest of the three except for instrument-only privileges.
Privileges under 61.215 are limited to ground training and endorsements for knowledge tests. A ground instructor may endorse an applicant for a knowledge test (the endorsement certifies training or home study within the preceding 2 calendar months, i.e., roughly 60 days) and may conduct the ground portion of a flight review. A ground instructor may not log flight time, may not endorse anyone for a practical test, and may not act as a flight instructor.
Recent experience (61.217): after the first 12 calendar months, the holder must have completed a renewal test within the preceding 12 calendar months to exercise privileges. Recordkeeping under 61.189 requires signing the logbook and retaining a record of endorsements for 3 years.
Trap: questions love the phrase "certificate expires." A ground instructor certificate does not expire; the privileges lapse without the renewal test. Another favorite: confusing who may sign a knowledge test endorsement versus a practical test recommendation.
Worked rule: certificate issued 14 March of a year → complete a renewal test before the end of March the following year.