Which Category of small unmanned aircraft must have an airworthiness certificate issued by the FAA?

Why →Under 14 CFR § 107.140, Category 4 operations require the aircraft to have an FAA airworthiness certificate, operate in accordance with its FAA-approved flight manual, and not have any safety defects.

The trap →Categories 1, 2, and 3 have progressive weight/injury-risk thresholds but do NOT require airworthiness certificates.

Field note →The four categories (1-4) form a hierarchy for flying over people. Category 1 is the lightest/easiest. Category 4 has the most regulatory burden.